You should plan to carry your junk with you. You certainly should not expect to leave spare wheels in transition. There is usually no room, and such material would be a hazard.

There is nothing wrong with passing on the bike repair stuff in a sprint. I never carry it with me in a short race. If you flat, your race is trashed anyway in such a short day.

Having said all that, there is no rule typically about reentering transition. People do it to retrieve helmets and the like. Just make sure you don't cross the timing mats if you have a timing chip.

What Art said, plus...

You should get used to preparing yourself for long rides on your own, without the 'crutch' of the transition area to bail you out of problems. Bring tubes, patch kits, allen keys and a pump/CO2. Know how to use them. When you step up to longer races, you'll be glad you did.

Depending on how entry/exit to the transition area is set up, there's the possibility that it could screw up chip timing if the race uses chips and the timing mats are set up where you'd have to duck back into T1.

You can enter the transition area as many times as you little heart desires.

However, there are two (three) major factor here that you must consider and which may complicate matters greatly.

1. You must complete the course in full. This means that if you go off into the transition area, you must re-enter the race where you went off. This could pose some problems as coming into transitions is not usually the same as going out.

2. Timing chip issues may also arise. You will most likely through havoc to the timing. Reason why they ask you not to step over the matts before the race.

3. It will surely be slower for you to go into transition and change your wheel and so forth than carrying a spare and a co2 and doing it on the course.

By the way, what makes you think that you will flat next to the transition area? Might as well leave a tube and c02 under a tree on the course.