Hi UCWarrior,
I just had my first surgery this past November, so I can really relate to where you're at right now. I only had to wait about three weeks between when I decided to have surgery and when it was scheduled, but the anticipation drove me crazy!
I wouldn't worry too much about supplies ahead of time. The types of products that you'll prefer to use can vary greatly depending on how your stoma turns out (for example, if it sticks out really well, you will use different barriers than if it's kind of an innie). My experience was that the stoma nurse at the hospital was extremely helpful in getting me setup with some starter products and then also with the home nurse, who helped me with ordering supplies and talked to me about various products. There are lots of different things that you can try (and companies are pretty willing to give out free samples of stuff), but it's sort of a trial and error process that you need to do once you actually have your stoma.
I think maybe the biggest thing that was helpful for me to know ahead of time was that it is okay and pretty normal for your emotions to kind of go crazy prior to surgery. For me, it was a hard adjustment to go from trying to do everything to avoid surgery to accepting that surgery was the best and only option. I felt a weird sense of sadness at the thought of losing something that had been a part of me for my entire life. I think I just had a general fear of the unknown and anxiety about the fact that this, unlike every other thing that I tried, needed to work. I had a hard time having faith in a good outcome since every other treatment that I tried was a disappointment.
All that said, I have absolutely no regrets, other than I just wish that this whole j-pouch process had started earlier and would have been able to spare me a lot of suffering. My life is so much better and I'm sure it will be the case for you also. Feel free to ask me any specific questions that you have