Right when you need it is when you don't have it. I'd always keep one bow of bullets. I have a fav setup with a couple of rocket pod and engi gear. If i'm gonna be a solid pilot i'll just use this armor. If not i'll unload my whole loadout into it. Then switch back to infil.
OFN we've been wanting vehicle trunk favs since beta.
Wrath truck for infils is very nice. I teamed with another cloaker on markov recently. Not squaded cuz we are both solo players on that server. But he sent me /tells informing me of where his wrath was stashed. Which he told me had health kits and bunch of frags, plasmas, and jammer. We worked out of that guys trunk for along time. Essentially it was our mobile invisable locker.
Every so often when i jack a vehicle i check the trunk. Rarely has anything other than what comes stock. But sometimes ppl use them. If i'm takin the time to go threw the trunk. Don't wanna decon the vehicle yet cuz i need it for distraction. I destory all the ammo. I did this once and then proceded to do my thing. Then d00d comes out and notices his vehicle was jacked. So he pulls out his REK and jacks it back, then leaves in it. Goodluck! ...with no ammo.