When I teach collective/uncountable nouns–usually as a consequence of teaching the distinction between “fewer” and “less,” and between “number” and “amount”–I find myself thinking “I should describe a collective noun as something you could take from your roommate without them noticing!”
I would like to note that I don’t actually traffic in that practice unless one of my roommates offers (except for shampoo. It was an emergency), but that’s where my mind goes. A splash of milk? A palmful of conditioner? Collective nouns! Not noticeable when removed! Countable nouns, in contrast–one or five candy bars, a lightbulb, (this premise stopped working when I considered things like grapes and paper clips, but countable hypothetically versus easy to count is a different discussion).
I haven’t tried this out on any students yet. Mostly because I don’t want them deciding that I’m a secret thief.