You can get those 800ml shaker bottles very cheap, perfect size for a bottle of spirits and you can use them for water when empty, but it's important to note that where everyone says mixers from Co-op, note what @LR10416 says - they're very specific and limited mixers. I'd assumed I could get tonic but the manager (they happened to be in the shop) told me they're not allowed to sell it.  At that time they only had coke or something else (maybe ginger ale) and I wanted something to go with g