Back in the day when bands were usually a gang of mates, a drummer I played with (through several incarnations of a few bands) was exactly that, we were best mates and used to hang out, go to gigs, take funny little pills, get off with girls, eat kebabs, etc blah blah..
This was all, I believe, reflected in our playing as a "rhythm section" if you want to call it that. We'd just naturally play stuff, lock into grooves, jam things and develop them into song structures, whatever.
I somehow doubt this kind of way of going exists much now, (tho I'd like to think it did)
Anyway good plan to try a "bass and drums alone" session and hope it is productive..
In your case I guess I'd make a mental note in advance of a few things or areas you think would be useful to work on.
I'd start off with just jamming with some bass line ideas and go from there...