I have tried eating from the oatmeal packets directly. Can work since they even give you a fill line for reference. However, they get cold REALLY quick. I switched to using a Titanium Mug from Snow Peak. It keeps the oatmeal warm while it hydrates the oatmeal. This was necessary for me since I eat oatmeal for breakfast. When it is 15 degrees outside, you don't want to old mash. I add two packets at once to the cup.
I also got a H300, which nests inside the H450 so I can also drink hot chocolae. I hope this helps.
Ti-Double H450 Stacking Mug
The Ti-Double H450 Stacking Mug is made of Japanese titanium utilizing a historic manufacturing process. With its double-wall insulation, the H450 Stacking Mug is designed for hot and cold beverages. Pair the H450 Ti-Double Stacking Mug with the Ti-Double H200 Stacking Mug or Ti-Double H300...
snowpeak.com
I also got a H300, which nests inside the H450 so I can also drink hot chocolae. I hope this helps.