I'll be going to JRTC soon for 11B for 3 weeks. What should I bring? Any tips?

Mosquito bar!

Got back from the box in Feb. had a blast. Embrace the suck. The training is only as good as the effort you put into it. Lots of bug spray, baby wipes, and the normal stuff for the field. And bring some money if you can get out the back gate of the box there is a mom and pop food trailer that makes great food. I think it's on route 29. Now to be fair my unit was OP4 so we had a lot of freedom and no rules of war. If you are OP4 refrain from killing role players they like you get kicked out of the box for 24hrs. And they don't get payed for the day so they will get really mad lol. We found this out cause our fisters "shot" the city mayor for selling info to the SF unit we were fighting.

Went to JRTC in January this year. My advice; follow any packing lists, and prepare for the weather. It rains down there a lot! Ziploc bags, and all your rain gear is a must. If you smoke, the grab between 1-3 cartons of cigarettes (people will bum from you, and even offer to pay you money for a pack of smokes. One soldier paid over 30.00 for just one pack from one of my buddies); and about 5 logs of your favorite dip(there will be times when you can't smoke). For example, when you are moving at night, etc. JRTC in January sucked, mostly because of the freezing cold, and it was wet, but other than that, I had a great time, shooting op4, and pulling security. Best of luck to you.

Having been assigned to JRTC 26 years ago besides the bug repellent, TP, and other essentials you might want to bring a book since as BLUFOR you will probably be "dead" and at a casualty collection point.

Look for some non scented baby wipes. Use them. Daily.
Take some sun flower seeds or other licky and chewy that you like but remember you're going to have to hump it.
Some type of electrolyte mix to help replenish what you lose. It'll help with drinking all the water you should be consuming. Nuun tablets come in bottles that don't weigh a lot and don't take up a lot of space. Cerasport. Something like that will help you in the summer months.
Bug spray.
Good socks.
Deck of cards or other card game for the down time. Cheap. Doesn't take up a lot of space and doesn't weigh a ton.
Ziplock/ waterproof bags.

Get in shape. Lots of hills to walk up caring a weapon system never to be fired because you will be killed when you reach the top.

Beware of the poison sumac

I agree with the baby wipes. Don't do what I did in Kuwait (18 years ago) and try to hygiene your ass with hand sanitizer! I thought I was dying!

As little as possible...But bring the basics, I didn't bring civilian clothes. I didn't need them turns out. You'll definitely need basic issues. Above all bring an open tentative mind, a closed mouth, a willingness to put others before yourself. Leave the humor at home. This is a great experience!!!

Bring Mio or some other type of water flavorer. You'll be so sick of water you'll go bat shit crazy. If you're going May - Aug, don't bring a single shred of cold weather gear or a sleeping bag. Can the wet weather gear as well, you'll be so sweaty it won't matter. If you got room, fill up snacks, you won't get a meal while in the box that doesn't blow (or all MREs). Finally, of you got a little space left over, bring a battery powered mini fan. Trust me, it'll save your fucking life when you get to sleep.