What can I do with white mugs that I don't use because they are too th

Stack them with small plates and candle sticks from goodwill...add a larger plate or bowl ....paint if desired for uniform look, can be used as bird feeder or succulent planter

Some diners love donated mugs.

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You might "marbleize" them and give them away as love gifts! Here is a tutorial I did on marbleizing mugs for gifts. Hope this helps. It is about other things too, but the white cups are listed. Just skip down to them. https://www.hometalk.com/diy/craft/holiday-gifts/surpise-your-valentine-34812819

Donate them to the Goodwill.

I use old mugs and tea cups for planters for my succulents. They don't require a lot of water but you do need a few small pebbles in the bottom to aid drainage.

These make wonderful little flowerpots and vases. Put a decal of something masculine like a duck, a dog, a horse, a horseshoe turned up for luck, and you have a great gift for Fathers Day. Perhaps you could make enough for a Sunday School class, a senior citizens’ center, your neighbors, or your relatives. It’s so hard to find a little something of value for men, and I think this would be popular with guys. And post your process on Hometalk! ☺️

Put them in a shoe box and use them to organize jewelry, craft items like beads, and small object that can be corralled.