I do not own any glass plugs, but I generally use my steel ones (Njoy Large and 2.0) without lubricant. Inserting them in the shower while they're wet seems to suffice for me.
After a few hours, they seem to gain a coating of natural mucous. Okay, that's kind of gross sounding, but it's great since it doesn't dry up like water-based lube, and it's not oily feeling like silicone.
As for silicone plugs, I've not kept those in for more than a few hours, but I do find that they become pretty dry within that time period. I wouldn't sleep with one in as I'd be worried about it sticking to my insides (and not like oatmeal, either).