what i usually do is before a show, i give songs code names, for example, wit metallica- fade to black-F.B, Sad but true-S.T etc.
This method is also good for bands that have a huge back catalogue, and that u r less likely to know what they're going to play.
A easier method for bands that just have on album out, or two is to just write down the track numbers of the songs they play from the album, for example, for trivium (tonight!!!!
Rain - 02, A gunshot....-06 etc..
u could record these on a piece of paper, on the ticket in pencil, or on your hand