Hmm. Let's see... last session was yesterday, so this should be reasonably fresh:
3.5e SRD (formatted, printed out and split into Rule Book, Spell Book, and Item Book)
3.0 DMG (for XP)
Oathbound campaign setting (I just transferred the campaign over to Oathbound, and am currently running the adventure/campaign in the back)
Psionics Handbook (two of the PCs got psionics as arrival gifts, and one of those got interested in psionic tatoos)
I think that's it. I also kept Minions: Rebirth, Arms & Armor, Arms & Equipment Guide, Mindscapes, and Book of Eldritch Might I and II on hand, but didn't actually use them.