My car's cup holder was made for very large cups only and has open sides meaning anything smaller (fast food cups, bottled water...) just falls over when taking a turn.

The inner walls are slightly tapered in to form fit fast food cups.

So I designed this adapter. Works great with all but large drinks which work OK without the adapter.

Since it has walls all around even smaller items can't tip over.

Could also be used to hold keys, change or a cell phone.