Whatever you want to put on the Jamba Bar works.
Well - almost whatever; it has to be a game object that is somewhere in your inventory.

I've used it for click activated quest items.
Have a single character drag their item onto the bar.
Which has each of the others do the same.
Then (via a mouse Repeater Region) over the entire frame, click the item on any toon and they all click it too.

I've also got the AV Trinket (which hearths you to just outside your last flag by your general) on the bar.
It is definitely not one of the two best trinkets, but it is useful for the teleport feature.
Click the trinket once on the bar, and you equip it.
Thirty seconds later, your toons can use it (via another click).

I've had Flasks and Stat foods on the Jamba bar.
You could go with your Hearthstones if you wanted.