We used garden grocer 3 weeks ago when we stayed at BC. They were great - highly recommended. But with the marketplace there, it wasn't really necessary. The prices in the marketplace didn't seem different enough to matter and they had different options for cereal, cookies, etc. Not many, but enough to satisfy our needs.
If you are just looking for milk, cereal, fruit and maybe some cookies for bedtime, the marketplace should do it. And if you flying, I'm not sure how successful a packed cereal box will be!