I took a totally ''winging it'' approach to sailing... after a summer of learning on a dinghy, spent a year refitting a 22'' MacGregor (very similar to the Catalina from what I can tell), and the first day she was in the water was to depart on a 4-month cruise from the northern Chesapeake to the Florida Keys.
Some of the best sailing I had the entire trip was on the Pamlico and Albemarle... a 22'' with decent equipment should have a great time out there.
Things you might consider: (some of these have been mentioned already)
VHF (a must in my opinion)
Extra fuel and water
What is your galley like? The Mac didnt originally have one - I had to add water tanks, stove, and sink.
Check the head (I assume its a portable type?) nothing worse than dealing with a leaky smelly head for a week... one with a 6 gallon capacity should easily last 2 people for a week.
Be prepared to get hooked on the sailing life - the day I got back from my trip I started looking for the next bigger boat to be a liveaboard