i have size 13 feet will they fit?

A piss bucket for the tent or when you are in deep playa and there isn't a JOTS for dozens of feet. If you make the hole big enough you can share it!

They make good scrap/ trash cans too. at ByB we use them at the bike stands to deal with the leftovers that no-one seems to take.

Maybe a Sumo wrestling suit??

pee spot and or punch container (not the same container ;-P). onsite artwork. large mask (after poppin some holes for air). wash-up spot? Thinking they could be more useful for lots of things later on too.

I have found both 2.5 and 5 gallon water bottles quite useful as containers for the brown water collected from the sun shower and kitchen. When the bottles are filled with either potable, non-potable, or brown water, they make excellent camp weights. Put them in tents, at the corners of tarps, or as anchors for light rigging.

Smaller water jugs with handles can be rapidly deployed to pin down loose gear during windstorms. Fill them with water or sand. Cut a quarter diameter section from the top down the spout opposite the handle and use them as containers for hardware, tools, food, light bulbs, etc.. Carry one around when you strike camp to collect loose equipment or trash.

Put a rope light or christmas tree strand inside blue plastic bottles and they become cylindrical beacons ideal for camp illumination and playa navigation markers.

that's just a few of MANY MacGyverish tasks at Black Rock.