Consider a second battery. It's always better to have a spare.
Consider a hydration system, either standalone or built into your vest. You want to carry water into the field and drink regularly in the dead of summer.
Don't buy cheap ammo, don't use anything below 0.25g.
Good base layer (sweat-wicking shirts, underwear) and proper socks make for more pleasant summer play.
Save up for transition from hicaps to locaps or midcaps. You will make the switch after you find out how annoying the rattling is. Unfortunately, G36 locaps and midcaps are usually more expensive compared to other types of mags, even when it comes to the economy box sets.
"The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."