As a first order approximation, the amount of money a person spends is a good reflection of how sustainably they live. It’s not an exact correlation—environmentally negligent junk food costs a lot less than locally-grown produce—but the ratio tracks well for most human carvings and their planetary impacts.

I’ve never been much of a shopper, so spending little money isn’t difficult; and ever since my time in Haiti, I’ve made a personal parlor game of celebrating days of spending zero dollars. The Awkward Poser’s folly against the bombarding temptations of our consumer economy. Still, even I am not immune from the adrenaline jolt of savvy shopping.

It’d been a tough week. Three days of drizzly rain. A dear friend in Worcester in and out of the hospital, then back in. Finding a new tenant, off-season, after one suddenly moved. Jumping through hoops with the city arborists to remove a tree that’s shearing my neighbor’s retaining wall. A family member in Utah lost in a coma. The usual stuff of life: sliced grim.

I needed a walk. Fresh air. Heavy-breathing at the gym. I also needed spackle to repair damage in the empty apartment. $6.99 at Whites Ace Hardware in Porter Square.

I’d squirreled a $5 coupon issued from a different Ace Hardware in my wallet. “Will you accept this coupon from another Ace?

“Sure thing. It’s a corporate coupon. That will be $1.37.

“How’s that? The spackle’s $6.99; the coupon’s five bucks.”

“First, I applied the 10% senior discount. Then subtracted five dollars. The sales tax only apples to the remainder. That makes $1.37.”

“Wow.” Amazed how the clerk applied benefits I didn’t even know existed, and then tallied them to my best advantage. I walked out of store whistling a happy song. The emerging sun seemed a little brighter, my step a little lighter. The jaunty satisfaction of such sweet purchase. Was there ever a day when a tub of spackle delivered so much joy?

Of course, White’s Ace Hardware won as well. I may not shop often, but I won’t soon forget this great deal. I’ll be back.