Yep, I grew up here so I can give you some recs although it is a kind of small town where things change hands often so could be a few changes since I was home at Christmas:
I don't know what you will be doing, but I imagine it will either include a day hiking or on the lake, etc. If you are boating on the lake, or just spending time, may I suggest getting rotisserie chicken at arrowhead market and some sides (they have great mac and cheese normally and I like the potato wedges and other stuff too) and taking that for a lunch or dinner, they have a dock, too fyi. Also you should check out Lakeside Creamery for really good homemade ice cream they even have a dock, with a LONG set of stairs.
You should get pepperoni rolls at arrowhead or somewhere else in the area they are a specialty of this area of WV, PA, MD (originating in Fairmont, WV). They have them at most convenience stores in the area.
For "high end" your best bet is Pine Lodge.
Brenda's Pizzeria has good huge booklyn style pizza, view of the water.
I think the BBQ place I forget the name on 219 in McHenry isn't too bad, it is kind of sweet BBQ, but good, better for take out.
In Oakland there is an antique shop that has a soda fountain in the back that serves breakfast, it is a local thing, if you are interested. It is just a greasy diner type place serving up bacon and eggs, you wait for a seat, if they don't know you they give you a menu, but it is where the locals go, they have good milkshakes and homefries and etc. It's called Englander's.
This is actually mid atlantic, if you look up Deep Creek Lake, there is another post I wrote on there. And there is actually at least one other Garrett Countian on ChowHound, I know of.
You HAVE to get yourself to the amish bakery called Sugar and Spice in amish country on 219 South. Closed Sundays. They have incredible homemade doughnuts, better than krispy Kreme when fresh, and wonderful baked goods and fresh breads and pastries. Pumpkin rolls, snitz pies, whoopie pies, fruit pies, it is good stuff.
The Cornish Manor in Oakland is another good more upscale type of place, I don't know what days they are open you might have to call I think it is Sunday that I always try to go and they aren't open.
If you are in nearby Ohiopyle for rafting or something in Confluence there is an excellent place called The Rivers Edge worth the drive from Ohiopyle. In nearby WV if you are headed that way (less likely when not ski season) in Davis Sierriani's has some seriously good homemade Pizza and there is also a place there called the Purple Fiddle that is fun.
I haven't been to the Savage River Lodge recently, but it used to be really good, and they do nice fishing and rafting trips and etc and is a great place for dinner after a day out, but is a bit of a drive.
Anyway I would cross post on the midatlantic or ask chow to move your thread there. Or at least search that board for some threads, have fun.
Oh and for drinking outdoors even the locals like to go to bar at Uno's its a chain, but the outside bar is fun. They also have an outside bar normally on Glenville Road at the Silver Tree. During tourist season call ahead before you go to the fancier places most will put you on the waitlist. Unfortunately there isn't as much there as there used to be in terms of high end, or at least no recent developments that I know of.