As someone new to long-distance rides this question perplexed me for a long time.  I am not one of the crowd that is keen on wearing skin-tight cycling shorts.  (I understand, though, this style of clothing has evolved in cycling circles because it reduces the wind induced drag on the rider by some 3-5%.) I checked the bike catalogs, went to the old standby's of WalMart and Target and finally bought a pair of cargo shorts.  I rode with these for several rides only to discover comfort was something that would become a prime importance when riding 75 miles day after day.  I went back to the bike catalogs and found a pair of "baggy" bike shorts for $45 which also had a chamois in the inside shorts.  I tried these...  Still not satisfied I went back to the bike catalog one more time and found a pair of inner shorts with a chamois.  I found these worn inside of the cargo shorts made a good match for me.  They were not tight, were reasonably long, and as it turns out, very comfortable.

Shirts were another big question for me.  The new cycling jerseys are advertised that they would wick the sweat away from the body and allow it to evaporate quickly.  Having broken any semblance of a budget I was not sure I should try to afford any for this ride.  So I pondered this for some time also.  Eventually I bought a soccer jersey that was reasonably cool.  In addition I also took several imprinted t-shirts which worked fine.  On my next long ride I might purchase several of the cycling jerseys, but the t-shirts worked fine.

Shoes...  The type of shoe is determined by the style of pedal that is on the bike.  Since I have the older fashioned strap type pedals on my bike I purchased a pair of running shoes for $10 at WalMart.  These worked fine for me.

Gloves can make or break you when it comes to riding.  My first pair were lightly padded gloves which were fine for shorter rides (<30 miles).  I realized I was either going to have to pad my handelbars more or spend some bigger bucks for a pair of gloves that were more padded for longer rides.  So it was back to the bike catalogs again.  I found a pair which had three layers of foam padding in the palms.  These suffised, but after riding for 4-8 hours bent over, your hands can still become numb.  For my next long trip I may buy a pair of gloves that have HFS liquid padding in the palms.

Finally don't forget the helmet.  I saw just about every type and variety of helmet imagineable on the ride.  The first helmet I had was probably 15 years old and had very few vents on it.  It would get so hot I would begin to feel sick on some of my earlier rides.  I opted for a Bell Mystic (you guessed it - WalMart) which was reasonably good.  One thing to check for when purchasing a helmet is to make sure it is approved by all of the helmet approval agencies.  I may replace my helmet before my next long ride.  Even though this was comfortable enough and was reasonably cool when you are riding a long distance on a hot day a helmet that has LOTS (20+) of air vents is big asset.

Recently someone at work, who is interested in taking this ride, asked me how did I train for a ride like this.  The answer I gave him was slowly!  Actually it was very simple.  Start out by riding 5-10 miles several times a week and gradually working up from there.  I have seen sites on the internet that gave specific guidelines for riding each week and increasing it to 100 or more miles per week.  The type of ride that you are anticipating will ultimately determine how you should train.  I met one person who had ridden 3000 miles in the previous 9 months.  Others, on the ride, told me they didn't train at all prior to the ride.  For my training I would ride 10 miles each evening after I got home from work and occasionally up it to 16 miles.  In March I rode 100 miles, April 200 miles and in May 200 miles.  I rode one 70 mile ride in May to see how I would respond and found out the hard way how much you should drink.  When it came down to the actual ride I felt like I did very well.  Since I had all day to complete the ride I could go at my own pace as long as I wasn't with someone.  I could push it very hard or take it easy.  Some people would start out very early
(6:00 a.m.) and take it easy.  I heard of one guy from a previous year who would wait until about 9 or 10 a.m. to start and then pedal like crazy and passing everyone, just because he like to pass people and still arrive early!   Just make sure, whatever you do, you are comfortable on your bike and are able to ride at least 10 mph for several hours - preferably faster.

What type of Bicycle?

I have never purchased a new bicycle before only used ones so when I started looking for a new bike I tried to do my homework.  One of the questions that frequently arose on the BAK message site was what style of bicycle should I purchase?  Last year when I considered BAK I had looked at a hybrid bike.  It is built like a mountain bike, but has some of the features of a road bike.  After reading the BAK site and thinking about it for another year I decided I would try to get a touring bike instead.  This has a wheelbase 3-4 inches longer than a road racer which doesn't force the rider into quite the folded position that the racer does.  Additionally the touring or racing bike places the rider into a more streamlined position when it comes to riding into the wind.  It does have it's drawback in that it can leave your back hurting at the end of the day.  One comment I have read is the touring or racing bike allows the rider to have many more positions on the handlebar that the hybrid or mountain bike does.  I did see one mountain bike, though, on which  the user had installed a special set of drops on the handlebar ends that converted the bars into a dropbar like a touring bike has.  Knowing the above factors I went to the Bicycling Magazine website's Bicycle Finder.  After entering all of the criteria it returned with the Raleigh R300 touring bicycle. I found a new 1999 model in town on closeout for $500.  It had a 21 speed Shimano gear set and STI shifters.  The rear cassette was a 13-25 with the chainrings being 52, 42,32.  I later purchased an another water bottle cage and bottle to give me 2 water bottles, a frame mounted tire pump and a small (to small!) underseat bag and a good cyclometer.
 
 

What would I do different?

A lot, but not much!
I would not take as much.  I suppose I did not use half of what I took.  Fortunately that half didn't include the kitchen sink or whatever made some of those bags so heavy!
I might ride slower, I said MIGHT. I like to be able maintain a higher average mph, I guess so I can stop more frequently for pictures!
I would take more pictures of people - this is what the ride is all about.
I would attempt more centuries - At least one more!
I would take the suggested side trips. I missed a really good one at St. Benedict from comments that people made.
I would TRY to slow time down.  For one week, no email, schedules, meetings etc!
I would try to enjoy it more if I could!