A small silicone cup can collapse and nest along the bottom like the S2S x-cup. I have used this cup to fit my mug along with a lighter, wipe, fuel can and BRS: https://www.amazon.com/gp/product/B07PT5H126/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

But I found I only use the cup in the morning to have coffee and oatmeal together. So I stopped using a cup and instead use a mylar bag to eat out of while using the cup for coffee.