You are going to want to sell all the Junk items you come across as well as any extra food items you are not going to use or are maxed out on. I would suggest buying outfit items and weapons from the equipment vendors because you will need those for other achievements as well. Also go to Toms Rhinoplasty and buying the Hasslehoff nose for a good chunk of cash for another achievement later in the game. This should be fairly easy to get without trying to specifically try for it.