It's difficult and/or impractical to store some things in quantity so there might always be a need to barter. Plus, in some situations, I would probably welcome the opportunity to trade the fruits of my skills for the fruits of someone else's since it could lessen the number of skills needed to get by when there's no time to learn. One person might be a skilled hunter and the other might be skilled at turning hides into shelter and/or clothing. Let's make a deal!