x2 with pen and notebook. I started an Excel spreadsheet, but found that it was much easier to keep my feeding sheet near the enclosure. Each feeding I try to get the following information:

Date
Snake weight
Prey weight
cage temps
humidity
Notes - things like - she doesn't want the feeding or if I feel it's time to move up in feeder size, etc...

I've only been keeping a snake for about a month so hopefully I'm keeping the right information.