bind <key> switch_channels

Cycle through the channels that are associated with the current window. I am told that nobody but me keeps multiple channels in the same window any more, so I don't know if this will ever be useful for you.

Once upon a time, this keybinding used to “steal” channels from other windows, but everybody disliked that, and channels never move between windows any more unless you intentionally do that (with /window channel)