After fully ranking up a Keepsake, it's worth upgrading others to keep your builds versatile. An efficient way to do this is with the Keepsake Collection upgrade from the House Contractor. This allows you to swap Keepsakes between Underworld regions. Depending on your goals during a run, equip the Keepsake you'd like to rank up in the early areas. Switch to a ranked Keepsake later in the run.