For high current (but not REALLY high current) I've been going with high strand count #8 copper. This is
about as heavy as you can get before flexibility starts being a big problem.
AudioPipe makes some high-strand-count CCA (copper-clad aluminum) power wire for use with small audio
amplifiers, that's really easy to work with when powering medium current draw accessories.
I've also been using 6ga OFC for my battery harnesses where I need to run higher current and lower volt drop.
These reels have two small but handy compartments in them that close very securely. On reels terminated with
SB50, I usually put SB50 / PP35 adapters in them, so the cable is compatible with smaller gauge wire. This
comes in handy when I need to run modest current a long way, and am using the heavier cable not for the high
current, but for the low voltage drop.