I have a homebrew that I need to revisit and fix the formatting of for mixed heritage PCs, and the system I came up with meant that I had to give every race four traits. Some of these would be minor, like darkvision, but there had to be four. I went with a once-per-day refuse-to-die ability and a proficiency-per-day advantage on a roll of your choice, so that the one thing humans do best is push through the tough situations