Put all valuables in your carry-on - not your checked luggage. This includes cameras, MP3 or CD players. Checked luggage CAN NOT be locked - if you lock it, the security staff will cut your locks, if needed, to inspect your luggage.

Do NOT pack any film - exposed or unexposed in CHECKED luggage. Always put film in your carry-on baggage. Checked luggage is now being scanned with X-ray equipment that damages film - carry-on baggage is x-rayed at the security gate with equipment that should not cause damage to most film. If you use "high speed" film with an ISO rating of say 800 or 1600, you should request that you film be hand checked at the gate. If you put film in a clear plastic bag, it makes it easy for them to see what you've got. (But who uses film anymore? Everyone seems to have switched to digital.)

Digital still camera memories are unaffected by X-ray security equipment. However, it is strongly recommended that you carry on all valuables, if possible, such as cameras. More information here.

Video tape, either analog or digital, is unlikely to be affected by airport x-ray machines.

Each airline specifies its own carry-on baggage limits. We won't know what those limits are until we know which airline is transporting us to D.C. As a pretty consistent rule, most airline restrict you to one carry-on item of 22" by 14" by 9" outside dimensions. They typically permit one additional "personal item" which could be a purse or very small camera bag.