When working up high, it’s very, very important to stay safe and be certain that nothing falls. Even something seemingly harmless like a roll of tape or a pen can cause problems if it plummets 40 feet.
So, everything is either kept in a container (a box, a milk crate, etc…) or tied off to the rails.
Normally, one wouldn’t bother to tie off a can of iced tea, but this happened to be in a high traffic area (near the ladder) and clearly someone felt the need to stay safe. And keep their tea out of the cardboard box of water and soda we’d brought up with us. Anything in the main drink/snack stash is community property and subject to drinking by anyone at any time. But a can, tied off to a railing is clearly private property.