Oh, I can do it. Does it have to be nutritious, or can I make my own choices?
Going back to the Boston episode, she had a muffin (and coffee?*) for breakfast. I could get a pastry and coffee from my local Italian bakery for under $5; or a Dunkin Wake-up wrap and coffee for for under $4; or a bacon/egg/cheese & coffee for $4.95 (typical breakfast, so I know the price to the penny

); or oatmeal & coffee at McDonald's under $4. So, $5 for breakfast, all with tax.
Okay, lunch. McDonald's salad is, or was, $5.03 with tax; adding a drink at $2.13 comes to $7.16. Or at Kelly's I can get a roast beef sandwich (
bad Bay Stater for not liking seafood... oh, wait, it's Kelly's
Roast Beef!) for $6.25 and a soda for $1.95; with tax that's $8.75**. Or, since this is Anytober at Subway, I gat a footlong sub that would actually cover two meals for $5; add $2 for a drink, then tax, I'm at $7.45.
I think I'll go with the bagel sandwich and the chicken salad - so $4.95 + $7.16 = $12.11
That leaves me with $17.89 for dinner, beverage, tax, tip, treat (drink/dessert/etc.) Well, according to tv.com, some of the tips in the show say to order half portions, or appetizers as entrées... I'm going to cheat a little here

.
Olive Garden's never-ending pasta & sauce for $8.95

I couldn't get the menu to display on my ITouch, so for my drink I'm just going to go with the ubiquitous water with lemon

. The meal tax here is 6.25%, so for my convenience I'm going to calculate the tax+tip at 25% overall, or $2.26, for a dinner total of $12.25 - rounded up so I'm not tipping an odd number of cents.
Okay, subtract that $12.25 from the $17.89 I had left after lunch, and I have more than $5 left for my treat - a dessert, a decadent candy, a glass of wine... Personally, I'd hit up the Market Basket supermarket up the street from Olive Garden. They've got some lush individual pastries, and the Italian bakery I mentioned earlier would be closed by now.
Disclaimer: no, I never considered doing this before; all pricing is either based on actual purchases or researched while writing this post.
*I have the $40 a Day book around somewhere; I could get the actual detail eventually.
** where I calculated in my head, I tried to estimate high.