Self-Pollinating First Fruit

Hello all! We have a large, relatively undeveloped back yard on a hill that we are hoping to transition into a permaculture food forest slowly. Starting with what we have, we have a GIANT barrel container that we want to use to plant our first fruit tree, shrub, or vine while we continue preparing the rest of the property, it really is massive so could definitely support a dwarf tree or possibly even larger. What plant would provide the most yield for our space without yet having a second tree? I have considered a thornless blackberry or possibly a passion fruit vine. We would love apples but my understanding is our yield would be low with only one?

I am in zone 8a in US as well, so I really have access to many things!