We bought little tubs from Mothercare, with yellow lids. They fit up to 4oz of powder inside.
HERE: https://www.mothercare.com/Small-fr...ing=UTF8&m=A2LBKNDJ2KZUGQ&n=75699031&mcb=core
They have more here: https://www.mothercare.com/gp/node/n/75699031/278-3095884-6218530?ie=UTF8&compareListASINs=&mcb=core
When you're onto bigger feeds, Tommee Tippee do some pink tubs, but they're marketed as food storage, not formula storage.
HERE: https://www.olivers-baby-care.co.uk/tommee-tippee-baby-food-storage-pots.html
I've never had any of them spill open on me, but then I do store them stacked up in my changing bag
We can't use the normal storage pots with multiple compartments, because they're quite wide, and our feeding pouch in our changing bag is quite slim; once you have the thermos in it, it only leaves space for another thermos, so the pots we have are the most useful for us