Monetarily speaking, the cheapest place to get this is at the fourth shop in the first stage, Mini-Marts. As long as you have $9.20, you can buy the all the items. They are as follows:
- Chewing gum ($0.95)
- Chocolate Bar ($1.25)
- Cola ($1.80)
- Grape Juice ($2.25)
- Energy Drink ($2.95)
Buy them all at once (as in, before you leave the shop screen), and the achievement will pop.
Also, The Delicious Cup a bit before this store is the second cheapest with items totaling at $10.85, but really you shouldn't want to spend more than you have to.
Thanks to BiLLzThEd0n for pointing out that you can't buy more than one snack at once unless you buy them "To Go," which will have you eat or drink the item right away.