I've used just about every lens I own there except the DA 10-17mm fisheye as that has been a recent purchase. I've also used a flash. It was really helpful when using the Pentax F 100mm macro. It's not all airplanes, jets, and rockets. If you have a right angle finder you might want to bring it as well. Monopods are allowed, but not tripods. They even hassled me about a Ultrapod II.
Steven F. Udvar-Hazy Center is charging $15 or $17 now ( Can;t remember which), even for drop offs. This is to pay for an expansion that is ongoing. I haven't been there since they started, so I don't know whether this affects the current display area, or not.
There is a McDonalds for food, but I would suggest bringing your own and getting a locker for the day to store it and anything else you might bring.
Steven F. Udvar-Hazy Center Flickr Set
If you are looking to pick up any gear,
Ace Photo is out in that area and carries some Pentax gear. Their on line listings for Pentax are larger than what they have in the store so don't get excited.
They also carry a ton of bags from a lot of manufactures. If you have ever wanted to just check out different options, this is the store to do it as you have full access to the bags. You don't have to keep asking a sales person to see another one. Crumpler, Tamrac, LowePro, Kata, Tenba, Domke, Billingham.
Steven F. Udvar-Hazy Center to Ace Photo - Google Maps
Thank you
Russell