One shot supply ship?

Yes its a nice idea, putting in a couple of emergancy supplies and ordinance will boost its usefulness even more. As these can be used to boost the supplies fiven out, then when you return to a resupply depot with a space yard they will be repaired (re-filled) allowing you to spend them again to fill the ships hold, then next turn repaired (re-filled) again.

If you add a repair module to the ship then you won't even need to return it to a planet to be repaired, although some of us consider this to be a very cheesy stratergy that takes advantage of the rules of the game rather than the spirit

Its more than a good idea though I would suggest that you build the ship on a warship hull so you don’t have to mount cargo bays. I have such ships with any fleet that I expect to be on extended operations. Its also easier to pull one of these ships out of a fleet and replace it whilst still keeping the fleet on station

If you are going for huge hulled ships, then you might as well add a space dock to the repair bay, that way you can not only repair ships but also upgrade them as and when required.

I find it's a handy luxury to have a huge ship with lots of supply/ordnance storage in a fleet. That way, if I want to resupply the fleet while it's out in space, I instruct various ships to dump their supplies/ordnance on that one Supply Ship and next turn it will then share them out appropriately.

Beyond that, such one-shot Supply Ships are best scrapped or sent to the far edges of your empire to pick up supplies that would never be used otherwise (requires careful calculation of how much supplies it takes to get there). I prefer the 'scrap and rebuild' option myself.

It's Emergency Propulsion + Repair Bay that's really cheap

A supply ship with nothing else is great to resupply a fleet.
Don't send them back to a depot though, as they will suck it dry.
Send them to a planet with a spaceyard and no depot to scrap it, and build a new one. Not really worth the time to refil it the depot way.

Don't forget to do research into solar collectors so your supply ship can generate supplies on its own. I don't know if there's any ordinance equivalent, though.

organic vast for ordnance regeneration