Um how many figures are we talking here Tiby? Well mebbe bring one for each series, well obviously not all series, but kinda. Oh heck here's a list hehehehe 

G1 - Optimus Prime ( of course), Starscream ( encore boxed - there's your boxed criteria all done heheh) Soundwave and some cassettrons, Hot rod - he's easy to transform, minibots brawn , huffer & bumblebee, Grimlock, Trypticon a few micromasters, Bludgeon, Galvatron, Bruticus - as Omega Supreme has mentioned...same reasons as well
Beast Wars/Machine - BM Blackarachnia ( after all she's the more well known Femme fatale ever mass sold, arcee never got her own mold) BW Metals Dragon Megs, Rattrap, Cheetor, BW Optimal Optimus, Airazor, Silverbolt - where black arachnia is he goes. Oh and Megabolt megsy as well.
RiD - Trainbot combiners, Megatron and Omega Prime, Car brothers some of the gobot type minicars
Armada, Energon,Cybertron - Unicron, Primus - in planet mode for convenience in carrying. Some minicon groups, mebbe starsword and skyboom group. Cyb Scourge, Hotshot - Cyb and Armada, An energon Combiner group - mebbe a boxed superion or bruticus maximus? Scorponok and a Scrapmetal
Animated - Activators bumblebee, Starscream, blackarachnia ( for comparison) and V. Prime, Prowl, Swoop
BInaltech, MPs, Alts - MP Megsy, Smokescreen, Puma type Ravage, Mirage/Hotrod, Nemesis Prime
Classics/ TFU - Henkei Astrotrain, Optimus and Megatron, Starscream, Ironhide, Mirage, Bumblebee- erm you could also bring Magnus City
commander mode. 
Movie - Prime and megs, Bumblebee, starscream, ironhide and some real gear bots!
Well thats it.. hope this helps
Wanted AM partner Vanguard, Myclones Dirge, G1 Victory Leo, e-hobby Dark scream ( the black version), e-hobby Magnificus
Parts- AM partner Basher-side guns, G1 Actionmaster Elite Windmill's blades[I][B]