When we visited GNP a couple years ago, we ate breakfast in our accommodations (vacation home rentals), took picnic lunches and snacks for our days in the park, and ate dinner outside the park. The exception to this was the one night we spent at Many Glacier Lodge. We had a pizza for dinner at the Swiftcurrent Lodge which was nothing special. We had the breakfast buffet in the Many Glacier Lodge which was both expensive and not good at all. (I had heard about avoiding dining in the Many Glacier Lodge--I should have heeded the warning.) Since you are staying in Whitefish, I would recommend you eat breakfast and dinner in Whitefish and take your own food into the park for lunch. You'll have no problem finding supermarkets in Whitefish.

The Park Cafe outside the St. Mary's entrance to GNP is the place famous for huckleberry pie.

Re: Yellowstone, there are several places to eat run by concessioners inside the Park. We found the food inside the Park mediocre at best.

Would suggest the cooler your best option. Cody is a small town. Has 1 Albertson grocery toward airport)and a Walmart Superstore with a large grocery store, and a SubWay at the entrance.

Near Walmart (toward Yellowstone East Entrance from Cody) is a good Bubbas BBQ open for lunch & dinner with a decent buffet salad bar. Near Walmart again toward Yellowstone East Entrance from Cody)is a Chinese Buffett that is decent for lunch or dinner.
Cody has the usual variety of fast food places, Wendys, McDonalds, Burger King Pizza etc. Again Cody is a small town so there aren't alot of great resaurants.
Check tripadvisor for more info...

Re. GNP: Lots of restaurants and markets in Whitefish and Kalispell. Park restaurant is HIGHLY overated!!! Food in lodges is mediocore at best. Pack your lunches and eat outside the park.

Just returned from a wonderful stay in Whitefish over the July 4th holiday. Whitefish has a fantastic downtown area full of shops and restaurants/bars. We had a really great meal at the Craggy Range. From Whitefish to the entrance to Glacier, you'll pass by lots of shopping areas including one that has a really nice/newish Safeway. Stop there and pack your picnic lunch. You can get food at all the lodges, but it is not very good at all (as John said - mediocre at best, and even that is probably a little generous!).

We stayed in Whitefish and East Glacier Park last summer. As stated above, Whitefish has several large grocery stores. However, keep in mind that you may not want to leave food in your car while you are out hiking if you are parking in an isolated area which could attract bears. obviously, if you're parked at Logan Pass Visitor's Center, a cooler with food would be okay. If you're planning on being in the Two Medicine area, there is a fantastic Mexican restaurant in East Glacier Park, Serrano's. They are only open for dinner and if you're not there when the doors open at 5PM, it's typically an hour's wait. Here's a good reference for more detailed information about GNP:
http://www.hikinginglacier.com/about-glacier-national-park.htm

Also, you may want to consider ranger led hikes if you have concerns about bears:
http://home.nps.gov/applications/glac/inforequest/inforequest3.cfm

This is all really helpful advice! I'm taking notes on the itinerary. Thanks so much!

@1jar thanks for the tips on the grocery stores. We will need to stop when we leave Cody before heading to Yellowstone so that is great! Is the BBQ and Chinese place you mention still in Cody then? Or closer to Yellowstone?

@beanweb24 - is there only one Safeway on the way from Whitefish to Glacier?

@wave725 Serrano's sounds great. We will have to see if we can make it. Thanks for thoughts on leaving food in the car. I was thinking it would be safe in the car but will read more about it.

Thanks all!

Sorry for the confusion. The Walmart, Bubbas BBQ and the Chinese Buffett are all in Cody: at the Western edge...convienentt to stop at before heading up the road (West) toward Yellowstone East Entrance on Hwy 20

Here are some links;
ChinaTown Chinese Buffett
http://www.chinatowncody.com/codydirestions.html

Bubbas Bar B Que (Below shows location of Walmart and Bubbas Bar B Que on map. Bibbas is in the parking lot of Americinn Hotel, a good place to stay.

http://www.bing.com/maps/default.aspx?cc=us&Rtp=~adr.512 Yellowstone Avenue Cody, WY 82414

Bubba's Bar-B-Que (has BBQUE take out in sturdyreusable plastic containers)
512 Yellowstone Ave
Cody, WY 82414

(307) 587-7427
http://www.bubbasbar-b-que.com

Our family stayed in West Yellowstone for 5 nights. We also ate breakfast in our room, packed a cooler with lunch, drinks and snacks for the day and then returned to west Yellowstone for our evening meal. There is a grocery store in West Yellowstone, cant remember the name, but we bought everything we needed there including the cooler. We didn't wanted to waste time eating inside the parks at the restaurants since we had heard in can be crowded. We did have lunch in a little place near Yellowstone Lake, think it was the Lake Deli and General Store, sandwiches and it was fine. While in W. Yellowstone we at at Geyser Grill, Canyon Street Grill, Bear Country Bakery, and Wildwest pizza. The food in all those places was good, not great, but we had nothing to complain about. Wild West Pizza was probably our favorite, we ate there twice I believe. Only in Cody for one night and had an late lunch/early supper at Bubbas, it was fine also. Great food wasn't really a concern of ours on this trip. We were constantly on the move and really just wanted a quick decent meal at the end of the day, which is what we got. Have a great trip! Loved Yellowstone!