Fair enough those who buy bags of ice cubes: I wasn't judging you, just wondering!
Is there not such a product out there, though, that is effectively two ice cube trays that snap/clip together, so you could fill them with water, close a cap or something at the end and then put them anyhow in the freezer - just like any (very flat) bottle, until they are properly frozen - and can then be separated and the cubes extracted individually as required? Lakeland MUST have something like that - surely?!
Alternatively, you could get a pack of those little tiny lidded tubs from Poundland and make your own. Surely, if space is at a premium in your freezer, it's more convenient to be able to make however many cubes as you want at a time, rather than having to find room for a great big bag from the supermarket - isn't it?!
Failing that, if you do have room and plenty of advance notice, you can just put a lot of drinks straight into the freezer and then get them out well before you want to drink them!
Each to their own, whatever suits people's different requirements and conveniences best; I guess I'm just too mean myself to pay for something to go into the freezer, that I have to travel to fetch from a shop, when I can get the basic 'ingredient' free from the tap in the kitchen and put that into the freezer!