Are they communal or individual? I seem to recall seeing some of them with pad locks on them on a visit several years ago. Is locking them with a pad lock ok? If not, are there any issues with theft? Also, what are the option if all of the lockers are full?

The lockers near the parking lots are communal. No idea why a lock would be on one, though I have used a lock on my campsite locker before to secure valuables that I didn't want to leave in the car (convertible with a broken door lock).

I have never seen them so full that there was no room to store more food, though you might have to use one a little farther away from the trail head.

Make sure you mark your items with your name and expected return date or you may end up with a tag on your package notifying you when the items will be removed. My bear can that I used on my Lone Pine Peak trip, but did not use on my Whitney day hike right after was tagged a few weeks ago.

Unless you have several massive coolers to store, you should not have any worries.................................DUG