Actually, instead of typical "wrenches", get a hex bit set. You can usually buy a typical 4+ piece set for a reasonable cost. Then you can use them in power screwdrivers or a nice ratchet handle.
EDS, Hudy, Losi, Dynamite and OFNA all make some quality sets.
Steer clear of integy. Theirs look nice and are fairly cheap, but are very brittle and prone to breakage.
I use a lithium B&D driver. My wife bought me the wrenches and driver last Christmas and man, do I use them a lot! Been in the hobby going on 10 years... I should have bought these 10 years ago.
personally i always like to carry my nut drivers, and hex wrenches. its also a good idea to carry some CA glue and zipties! (trust me zip ties come in handy big time at the racetrack when you don't have the $ or your broken part isn't in stock)