For the sweat, try some deodorant/antiperspirant, works wonders *slight sarcasm*.
For periods, just be glad you do not have them yet and when you do, hope that you don't get cramps. If you do, keep an ibuprofen or something with you. Try keeping a small kit for that with pads (or tampons, whatever you end up using), ibuprofen, change of underwear, with you just in case (better safe than sorry in that situation).