You could drill out the handle and keep urban survival tools inside it! Like... A bus timetable, a lighter, a cigar, change for the bus.. The list (unlike the handle) is endless!
A hammer AND the willingness to prevail are all you'll ever need. Of course, you could replace the word "hammer" with almost anything, so there you go. Personally, I prefer the Estwing 24 ounce framing hammer with the smooth face, but I earn a living with it, so you urban prepper ninjas might prefer something different.
Plus they'll be laughing on the other side of their face when the zombie hoard is coming for them and all they've got is a tactical pen and a folding knife. Oh, and a keychain. P.S. painting it flouro green will make it more efficient.
Incidentally, I have a 24 oz Estwing straight-claw hammer.
Another fan of the 24 oz., eh? You get that little bit of extra oomph that is missing form the 22 oz. without all of the I'veblownmyelboout of the 28oz. I knew I liked you.