I keep a log for each snake with just three columns - date, event code, and notes. Codes are 'A'te, 'S'hed, 'V'et, 'W'eight, 'B'red, and 'O'ther. In the notes I'll write more information, such as what was eaten, the snake's weight on that date, why the snake went to the vet and what was prescribed, etc. If the snake is sold or has to go to the vet, I can provide the history easily.