What should I check during a final walkthrough?

Compare the home against both the original inspection report and any repair agreement, room by room, rather than relying on memory of how it looked during earlier showings. Run water at every faucet, flip light switches, test the garage door and confirm the HVAC system still works now that the home is empty or near empty. Photograph anything that looks off so there's a record if it needs to be raised before closing.