I sometimes use a plastic Ziploc brand bowl. They come in 8 and 16 oz sizes. I think the larger one weighs around 0.9 oz without the lid.

If I'm using my huge mug-shaped 1.2 liter GSI aluminum pot, I just drink out of it. If I'm using my flat 600 ml Evernew titanium pot or a beer can pot (for water only: hard to clean), then I use the plastic bowl.

Drinking out of the pot has an advantage in that the hot liquid helps clean it after a meal.