What this guy
>>148049 said OP.
I've played about 20 or so scenarios over the last decade (mostly Viper Scenarios). I started out with a 4-pod pack and used Army surplus web gear to attach to the pack then attach whatever I needed. Now I wear a nice 8-pack of 120s and the exact Camelbak you see in the pic. Nothing too fancy. The Camelbak can hold 1.5 liter bladders and has enough pockets to hold emergency tools and such for my marker plus candy, energy bars, etc.
I'm older and even though I am in excellent shape, I don't stay out in the mask-on area all day. There's at least one day break in there depending on how much paint I've been throwing then there's a shortish break before night-play. And my night play is only a few hours unless the game turns epic (there's beer to be had at camp).
What you wear in play shouldn't take too much thought. Take the advice here. The main concentration should be your camp set up - if you have a bunch of buddies going, have everyone bring their camp crap (tables, chairs, awnings, generator, camper if you have it...). And if your scenario has a final battle, just fill your pods and bring your extra paint to the insertion point. Have fun man.