They could be tasty meals or a snacks, such as biscuits.
Dave: Oh no! We've got no yums.
Joyce: When are you going to buy some yums?
Dave: You can always go and get some yums yourself!
Whilst yums can be anything that someone finds yummy, it is a popular phrase amongt foodies, particularly vegans. It is common for people to post pictures online of their food, tagging them as 'yums'. The word yum has only recently started to be used as a noun, it was previously just used as an adjective that meant tasty.
Here's a typical way of using yums on Twitter: