Some questions (half ironman)

I don't know bout bike computer. Yes you can wear a fuel belt. Stop where you want but iron man has lots of great stops with plenty to eat an drink. As far as penalty boxes I was freaking out bout that. What I found was unless your fast enough to compete for slots or win nobody cares. There were tons of drafting an passing issues in my ride but literally it was the slow folks just out to finish an I never once saw a judge. Just relax an have fun.

And...yes, you can use a bike computer!

The penalty tents were very evident during Ironman Augusta 70.3. They were the typical white topped, pop up style canopies you see at sporting events, etc.

I would not worry about penalty tents, cards, etc. unless you are in contention for top awards in one of the younger age groups, or a pro. Unless you are doing something that is creating a safety hazard for yourself and other riders (in which case officials will probably issue penalties or warnings if they see it), even in a world championship race, it's been my experience they rarely pay attention to drafting beyond the pros and top age groupers. Not that you should blatantly draft others for long periods of time, as that's just not good sportsmanship and can be dangerous in a crowded race if you/others are not experienced in group riding, but no need to be overly paranoid about it or risk your own safety (for example, going out into a traffic lane at a risky time to make a pass) to avoid getting a penalty or warning.