My thoughts? It'll be the same as whatever the historic equivalent was for that use-level of transportation. If slow and costly, expect valuable things that are difficult or impossible to produce locally. Spices, silk, gems, and artwork were all traded insanely long distances -- along with expert personnel. If transport moves faster and/or cheaper for some reason (say, wormholes or hyperspace) then we can begin to add bulkier commodities in approximate order of demand/difficulty. Since we live in the information age now, we should also count information as something to be traded, although it usually doesn't have to be shipped in hardcopy.
If people can move at all, then they will ship and trade things.