Depends if it's amplified power or if you're just using deck power. As for lights, that also depends if you're installing a huge 72'' lightbar or just some small little LED spots. I would say anywhere from 12 to 16 gauge.
I used 12 gauge for everything. I bought a roll of good quality speaker wire in black that is easy to hide but has the + printed on it to identify the positive and negative wire. I'm sure it's overkill for most items though.
Attached is a pretty good chart I used when I did mine. Another thing of note is that the watt or amp listed of the led light fixtures you get off of Amazon are way off from reality. It's so widespread I'm surprised there hasn't been a class action suit against amazon because of it . My 240 watt lightbar is 196.8 watts. My 120 watt sidelights are actually 21.4 watts. My 27 watt backup lights are 14.5 watts. I'm sure the lumens are similarily inflated, but I don't have any way to test them.