A second RG-6 cable. One for cable and one for the roof antenna which feeds the HDTV (I hate paying extra to the cable company for HDTV when I get more stations off the air) (My TV also has inputs for each)
I found that putting 4 plugs (2 duplex) in the J box behind where I expected to put the TV also payed off by eliminating the need for a power strip.
The cat-5 is unnessary if you plan to use WiFi (though that will not give you the fastest speeds). Wired is cheaper and more reliable in the long run.