I ran out of the house on Sunday morning with a $5 bill and a plan to pick up milk and four bagels. I came home with a half-gallon of milk, a single bagel and 24 cents in change.

“The price of flour is unbelievable,” the cashier told me when I realized I wouldn’t have enough money to cover all four unadorned bagels at 95 cents per.

I’ve written about the cost of gasoline and followed news coverage on $7 boxes of cereal and the run on rice. I feed myself and at least one other person daily, but somehow the escalation of food prices didn’t really hit home until Sunday.

My boss covers my lunch most days and I like to stock up on Lean Cuisine from Nestle (NESN) when it’s on sale for $2.

The rest of the time, when I run out for something quick, I usually grab a $20 bill. Or I use a debit card to pay for it. How much cash, I wonder, is flowing through my fingers by failing to spend in a mindful manner?

Every room in my house has bowls or cups carrying the loose change and bills I extract from my pockets each night. I usually get around to counting this when I’m about to go on a vacation.

I got into the debit card habit because I like the spending paper trail it leaves when I want to organize myself at tax season. I tend to round up my debit card spending to the nearest $5 in my checking account and every now and then “raid” the excess to cover the cost of an emergency dryer repair or some other unanticipated, utterly predictable expense. Bank of America (BAC) actually recognized consumers’ rounding up tendency and turned this into a savings program it markets as Keep the Change.

I figure paying cash and using a debit card puts me well ahead of those pulling out a credit card to cover their basic costs of living. But, hey, you never know. I could do a lot better.

So here’s my vow. From this day forward, I’m pulling out the smallest possible bill to pay for whatever I’m buying in cash. I’ll limit my use of debit cards to my twice-a-month grocery shops. I’ll get my daughter in on the act too, although she’s already pretty good at this practice.

I will stop short of writing down every purchase I make, although in really tight times in the past I’ve found it an effective way to cut back. I’ll report back every other month or so and let you know what happens.

Spend mindfully. Breathe deeply. Can I save enough to squeeze in a massage?

What steps have you taken to keep cash from slipping through your fingers? Weigh in on The Exchange.