I think it was the $4 milkshake that did it.
I had gone out to lunch at a gourmet burger place around the corner from work and ended up dropping $16 on a burger, onion rings and the milkshake. My brain - and my retirement savings plan - recoiled at the bill.
How much money am I throwing away by going out for lunch, I wondered. Answer: a lot.
Assuming you spend an average of $10 a day on lunch, that means you're dropping $50 a week and $2,600 a year on lunch. Lunch! And grabbing a burger or a slice of pizza or even some fancy wrap isn't just worse for my wallet than brown-bagging it, it's also worse for my health.
"Most of the time when you eat out, you don't get the fruit, the vegetables and the milk," says Amy Torch, a registered dietitian in Toronto and founder of Nutrition By Amy.
So I decided to start packing my own lunch from Monday to Thursday and then going out on Friday. And to make sure I'm saving money - it's not worth it if you've got lobster glazed in foie gras in your lunch box, after all - I have a weekly brown bag budget of $20.
This isn't much of a challenge, according to some of the dozens of readers who e-mailed me with their advice.
"You must be living in another world if you think it is tough to make your own lunch for less than $5 [a day]" one said, adding I could easily make a sandwich for half of that.
Others said brown bagging it for less than $5 a day has been the road to riches. "Everybody always wondered why I could take three months of vacations in Europe yearly, why I could drive a nice car, how I could handle a T.O. mortgage all those years. Piece of cake. Neither my husband [nor] myself did regular lunches or coffees out. We almost always drank the company coffee offered and brought our lunches," one said.
I'm going on the record to say I will gladly trade gourmet burger lunches for European vacations.
And I can also say that eating lunch on $5 a day is pretty easy, but not that easy. Readers' suggestions fell into three categories: leftovers, sandwiches and soup.
"I make soup on the weekend … a big batch of it," one reader said. Others pointed out that canned soup is also inexpensive. A tuna sandwich with a banana and a yogurt can also be put together for less than $5. And leftovers are pretty much free, depending on how you look at it.
But you can't have anything you want on a budget of $5 a day. While I was able to afford four chocolate pudding cups, since I found them on sale for 99 cents, I couldn't afford the granola bars I like to eat. In fact, most packaged food was off the table. On the upside, that meant eating way more fruits and vegetables than I normally do.
It also means being organized.
One reader said he and his wife roast a chicken with vegetables on Sunday night and use the leftovers for lunch for the rest of the week, making soup and a few sandwiches.
"You are not going to throw together a $5 lunch as you are running out the door," another reader warned me.
That's actually how the problem started. Usually I'm so pressed for time in the morning that I skip making a lunch entirely. I'm guessing a lot of people who go out for lunch have the same excuse.
Which is why I highly recommend coming up with a weekly lunch menu and then making each day's lunch the night before. That way it's there to grab when you've got a screaming kid who's already late for school pushing you out the door.
My lunch menu for one week consisted of staples like apples, bananas, yogurt and fruit juice, and for mains I had a tuna sandwich, a Black Forest ham sandwich, and two days of spaghetti, because eating the same thing every day is boring. Saving money shouldn't feel oppressive, which is how I feel when I have to choke down tuna sandwiches four days in a row.
But there was a problem. One of the best things about going out for lunch is that it means leaving the office. Eating at my desk can feel lonely and pathetic. It doesn't make a lunch break feel like much of a break when I'm still hunched over my computer.
That problem was easy enough to solve. I just went to the park down the street. Still, I went there alone, and found myself missing the conversation and camaraderie that comes with going out to eat with colleagues.
But I pulled an apple out of my bag, laid back in the sun and enjoyed the fact that while I wasn't with friends, I wasn't shelling out $20 for a hamburger, either. Besides, Friday was only a day away.