I've numbered my boxes, but only so I can tell if one is missing.
I should have written up a log of some kind detailing what exactly is in each box, but it's too late now. :-/
I have so few boxes I'm just labelling them, but the books are labelled by genre, size, and alphabetically. I got a little carried away. Plastic tubs go unlabelled - I will open them in September and be pleasantly surprised by what's inside.
Saturday & Sunday we didn't label the boxes from the garage at all... just boxed 'em, sealed 'em, and moved on to the next one, trying to get done as quickly as possible.