ground: large power cells reason i'm a science officer and out damage most tacts in pugs in elites that should not happen thats when i hit the cells if things go a lil awkward.
large hypos are a must for anyone for any ground combat keeps you alive you can use them when held by the vampire things sometimes they unlock the hold sometimes they dont.
shard of possibilitys 3 is better then one ok they dont do too much but are useful more damage more targets to distract an enemy essental for pvp.
gambling device reason simple improves crit chance and severity again essental for pvp works fine in pve definatly something to have if your a serious ground fighter and stand still watch it when it fails to work and the motion of your character
space subspace field modulator dont use in pvp alot of players use anti proton it takes you 400- anti proton resistant..
weapons battery mainly use when weapons offline or used full impulse coming out with no weapons power isnt too good
shield battery use if i need a lil extra shielding or shields offline
and if space depending on ships i use an auxiliary battery too auxiliary is used for hazard emitters aux to structural and when offline they dont function not a dangerous thing unless your in trouble then i use it and sometimes i use it for an extra power boost to give my abilitys and healing stuff which uses it more effect useful to have in bigger ships carriers cruisers ect
For ground I usually use:
The shard of possibilities, a stack of large hypos and a stack of holographic exocomps, and then I use the fourth slot for whatever I might need for the mission at hand, flashlight, Ophidian cane, Horta, etc. If there's nothing I think is particularly useful I'll pack a tribble in there. My MACO set comes with a shield heal, so I don't need a shield battery.
In space, each ship is different. But I usually pack either large shield batteries or combo shield/Aux or shield/engine batteries. Deployable turrets are also handy.