Clean your refrigerator condensor (behind, or under your refrigerator). You would be surprised how much more your refrigerator runs when it can't get rid of the excess heat.
Caulk, seal, wrap. (including that in-wall air conditioner that you have never covered before). When foaming around doors and windows, make sure you have the proper type. Using the high-expansion foam will make for a (not so) fun home repair project. Consider storm doors.
check up in the attic. is there any insulation there? No, i mean that question seriously. You would be surprised how many homes don't have attic insulation. How about the scuttle hole cover? Foam insulation on the back of it, and a weatherstrip around it will help seal it. Do you have pull-down stairs? They make foam covers for these, as those stairs are basically a sheet of 1/4 plywood on the face, and not very efficient at stopping warm (expensive air) from disappearing. Money well spent up here includes blowing in a layer of cellulose or fiberglass. Don't block ventilation at the soffits, however, or you may have worse problems than a cold house.
Stone foundation? Consider having the inside, from ground level up, sprayfoamed. (if you foam the whole thing, frost damage may occur to the foundation.) At the very least, if you have a concrete foundation, insulate between all of the floor joists, at the rim of the basement. Don't block off the bulkhead stairs, instead use foam panels directly on the upper edge of the bulkhead foundation walls. (under the bulkhead doors). if you block off the whole area, frost damage may occur.
Not all of these may apply to you, your mileage may vary, etc, etc.
And I am looking for some old water heaters, too.....