A chum is a happy friend.
A chum is probably a good friend, too, but the essential feature of chums is that they have fun.
Eating ice creams is a chummy thing to do, and so is going shopping. The high seriousness of a football match, though, calling as it does for deep concentration, might be too much for true chumminess except during the interval.
If you're in Scotland then to chum is very easy, because it means to go with someone. You could chum someone down to a canteen, for instance, or to the bus stop.
American anglers and birdwatchers go in for a different sort of chumming. This involves grinding up the smelliest sorts of fish and then either using the resultant gunge as groundbait (anglers) or for spreading the stuff, mixed with oil, on the water (birdwatchers).
This water-floating sort of chum generally attracts petrels and albatrosses:
Image: Southern Royal Albatross. Photo by Mark Jobling.
more than humans.
The last sort of chum is the most difficult of all to be because it would involve turning ourselves into Pacific salmon Oncorhynchus keta.
I couldn't honestly recommend it even if you could, as they are found so often in tins.
Thing To Do Today: be a chum. The word meaning friend appeared in the 1600s when it meant a room mate and was probably Oxford student slang for chamber fellow. No one knows where the word meaning fishy stuff comes from, but the salmon comes from Chinook Jargon (nothing to do with helicopters) tsum, which means spots or marks.