“ A casual remark by one of the party about something met on a previous adventure leads to a summons to and grilling by the Mages' Guild (or equivalent), probably resulting in an expedition back to that area to recover the things for study by the Guild. The party's presence will be 'requested' for this expedition.”
“ Often valuables is counted in coins, jewelry and magic items. Surprise your players by offering them cheese, wine, cloth and art as rewards and payment.”
