3/8" sockets will do most of the jobs a 1/2" socket would, at a much reduced weight.

Also METRINCH sockets & spanners greatly reduce the weight & size of a tool box. I got a set of METRINCH open/ring spanners, I wouldn't mind a 3/8 socket set at some stage.

A good quality multi tool (swiss / leatherman / gerber) on your belt will also mean not having to even open the tool box for small jobs requiring screwdrivers, small pliers, knife etc. Well worth the convenience.