I think it would be really nice (and appropriate) if certain vendors were available on the bridge (or other parts of the ship when those options become available). A computer terminal for things like uniform customization and basic weapon procurement would be very appropriate since matter replicators on the ships can make most of the things sold by vendors. You should have to purchase patterns vice actually having to go somewhere to buy a physical item. Once you have a pattern, you can materialize what you need (at the same cost of energy credits, of course) right on the spot instead of having to waste time going back to a station.
At the very least for uniforms, since I have a tendency to get bored with them quickly and like to change them often.