In the options menu select cheat codes and enter the following:

plus44-Unlock Travis Barker
hohohosoi-Unlock Christian Hosoi
notmono-Unlock Jason Lee
mixitup-Unlock Kevin Staab
strangefellows-Unlock Dad & Skate Jam Kid
themedia-Unlock Photographer & Filmer
militarymen-Unlock Colonel & Security Guard
jammypack-Unlock Infinite Special
balancegalore-Unlock Perfect Rail
frontandback-Unlock Perfect Manual
shellshock-Unlock Infinite Focus
shescaresme-Unlock Big Realtor
birdhouse-Unlock Inkblot Deck
allthebest-Unlock Full Stats
needaride-Unlock All Decks except for Inkblot & Gamestop Decks
yougotitall-Unlock All Special Tricks
enterandwin-Unlock Bum
wearelosers-Unlock Nerd
manineedadate-Unlock Mascot
suckstobedead-Unlock Zombie
sellsellsell-Unlock Skinny Realtor
newshound-Unlock Anchor Man
badverybad-Unlock Twin