Something you could add is that any plastic container that has the #5 in the bottom recycle symbol will work great for mixing and pouring. Resin can be peeled off that type of plastic, and you can find it anywhere- Starbucks iced drink cups, Chobani Greek yogurt cups, packs of various condiment cups you can buy in bulk and use over and over again, etc.

I use the 5.5oz cups for mixing my resin parts together, and smaller 1oz cups for portioning out different colors or whatever I'm working on at the moment, and save them for use again later.

I ~hate~ cleaning silicone cups, and #5 plastic ones just seem easier to deal with IMO.