I take notes/make sketches during sessions, and keep those all in a folder with my charsheet. The right margin of those sheets is all my resources--HP, ammo, spell slots, whathaveyou--that change a lot during the game, tallied and crossed out and rewritten through the night. At the end of session, the charsheet gets updated if they've changed.
(Most times they haven't, because the session's not ending mid-action, so the resources are going to come back to "full" during town-time or the like.) Saves the eraser-hole problem.