I'm not too familiar with mystery shopping. What does it entail and can anyone do it?
I could never save $1 bills

Sometimes it's the only thing I have to eat off of when I'm on call overnight. You have no idea how good a Snickers bar and a coke tastes from vending machines when its 3AM!
I should brown bag it more often though, i hear it saves a ton of money. I probably spend too much money on food
I think you would be shocked at how much it can save. Just even buying that snickers and coke at the grocery and stocking your locker would make a huge difference - especially if you buy it on sale.
My local grocery store has 24 packs on sale for 5.99 That's .25 a can as opposed to what, .80 a can from the machine? If you work 5 days a week, 4 weeks a month, that's $132 in a year... Don't even get me started on $4 latte's...
Mystery shopping is easy and anyone can do it. you sign up with companies and then apply for shops. They give you guidelines to look for, like were you greeted in 10 seconds, was the employee wearing a name badge, did they use the company's catch phrase etc. You then go back and write a narrative - not less than 100 words, not more than 500.
Sometimes they have you buy something, sometimes not, sometimes you buy it and return it an hour later. Items can range from a $2 card to a computer! (you don't get to keep the big items but rather, must return them)
Once I went to the airport, was escorted through security and did 11 different restaurant shops. I was given X amount to spend, reimbursed, and then of course paid around $12 a shop. It took me 2 1/2 hours, I wrapped all the food up and packed it in "my carry on" and ate for several days on it...and made $140 to boot.
once I had to get car insurance quotes for 4 companies online - that paid $60. Once I had to call a handy man service and ask a question - it only $5 but it took me all of 2 minutes.
Some companies will have you go to the movies and look for signage or trailers. Some will have you go to stores and check endcaps for displays. There's a wide range of things you can do.
It used to be all under the table. Now they are requiring SS#'s for tax reasons..
Anyway, when I'm short on cash...I look around for shops.
You pick the shops you want to do. Shop every day, once a week or once a year. HTH!