The folks in Beacon Hill are equally lucky to have Charles Street Supply, which has been in the same spot for more than 60 years and is run by the son of one of the original partners. It is old-school and crammed to the rafters, too. Both stores have almost anything you'd need in the way of cleaning supplies, tools, hardware, light bulbs, gardening equipment, seasonal items, and so on. Both stores also have all those things you don't need immediately but know you will need eventually, so strolling the aisles is instructive and strangely reassuring.
Both stores have seasoned, helpful staff who can talk you through just about almost anything you're contemplating doing. They might even come over and do it for you (if they like you or fear for your safety). Or they might give you the number of a good handyman.
But Charles Street has a slight edge because they have a shop cat:
Long may that tail of hers wave.