I don’t do overnighters, but like to bring plenty of tools/snacks/fluid on long rides in remote locations. I have a roll top saddle/bike packing bag that has plenty of capacity, but didn’t like it for my purposes (kind of awkward to get things in and out of frequently when on the road...I’d think it’d be much better for infrequently needed items like clothes and toiletries, as you use).
I now mostly use a half frame bag to hold my gear. Mine is an Acepac, which I bought because it seemed sturdy and a decent price, and I found it at the LBS so I was able to test fit it in the triangle. The advantage with that particular bag was that on my bike, the fit was perfect in that i could still hold my two water bottles underneath, snugly. In fact, the fit is snug in a good way...the bottom gusset of the bag hugs the mouthpieces of my water bottles, helping keep off dust. The bag has been great, has plenty of room for anything I’ll need...easy to access while riding.