That's why you use the gambit. That way you always have Libra on (unless you're in the middle of a fight), and you have the Accessory slot free for useful things.
That's also why I have Libra on all characters. If it runs out in the middle of a fight on the only character with it activated, I can't see the enemy's health etc.
The Bangle wastes the slot, in my opinion. I'd much rather throw an Embroidered Tippet or a Golden Amulet in there.
I always have these Gambits on someone: (in no particular order)
Self - Libra
Self MP <20% - Charge
Self - Protectga
Self - Shellga
Self - Bubble
Ally: Any - Regen
Ally: HP <50% - Curaja
And then you just edit the rest depending on what you want your character to do.