For my portable-assembly projects, I've used plastic biscuits and plastic or metal dowels.
Obviously, do not expect biscuits or dowels to maintain a planar surface.. If it must be flat and/or strongly joined, you'll want to add a backer board to ensure flatness and rigidity, and some draw-pull latches to secure the pieces together. Don't forget to consider uneven ground surface, so you likely should add some adjustable feet on this thing, or bring scrap wood to help level it..
For biscuits, I simply used a utility knife to cut out the size I needed from PVC lattice fencing (ie. 2" lattice kind, 8'x4' $19 at Lowes) & I use the knife to beveled the edges of the PVS so it slips in/out of the members' slots easily. I brad-nail or glue the biscuit into 1 of the members so they don't fall out. PVC also conveniently allows for some flexing during assembly of your pieces (rather than your product cracking), should your pieces warp a little bit over time.
Similarly, for dowels, you can use very small diameter PVC or PEX pipe (like for refrigerator water lines) & bevel the ends. PEX is a bit weak for flexing during assembly (AKA, fatigue).
You may want to look into beveled metal pins for shelving units, maybe plastic even exists (pin on both sides, often with a thin stop flange). These can be purchased loose from most hardware stores. To one member, I would secure the pin, either with glue or a sliver of wood for a tension-fit.