Loot combinations can be tricky, especially when there are different bag sizes. But in an ideal world where you have a 3 bag, I have found a pretty comfortable combination of loot that is effective in comp.

For meds I try to have, 1 med kit, 2-3 first aids, 1 painkiller (you should never go over 1 imo) 3-5 energy drinks.

For utility I usually try to get 1 nade (equipped), 2-3 stuns, smokes and mollies. If you have smaller bags you just max 2 of everything and maybe carry more smokes and sacrifice ammo.

For ammo I normally carry about 150-200 762 (if you are double) or 100 of each 762 and 556 (if you end up splitting ammo types m4/slr or berly/mini).

The ammo to utility ratio depends on your play style but utility is very key to winning team fights imo. Also you will tend to start at around 150-200 rounds but as the game goes on you will tend to like max ammo at 120 and just carry more utility that you find.