Keep in mind, there are no perfect boards, but try to always use the straighter boards and avoid warping boards. Also, Brandon and I have found that when it comes to picking out lumber at Home Depot and Lowes, they tend to stock up on fresh boards a few days before the weekend starts (so Thursday/Friday). And then, on Sundays and Mondays, the boards are usually really picked over and there isn’t a good selection. Just another tip to keep in mind!
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.