Instead of using a container to mix a small amount of epoxy, just make a mixing surface on your workbench using painters tape. Simply lay down strips, overlapping the edges so the epoxy doesn’t get on your bench. When you’re done, peel off the tape and throw it away. This mixing surface will work for more than just epoxy, you can use it for wood glue or any other material you need easy access to while working on a project.
Here’s a nifty tip—with a nifty tip—from faithful reader Don Ayers: Fill snap-capped sports water bottles with glue and stick them upside down in a hunk of 2×6. Now you don’t have to wait for the glue to run into the neck of the bottle, and the cap will control glue flow (and never get lost!). To holster the glue dispensers, cut holes in the base with a spade bit that’s a smidgen larger than the cap’s diameter.