While the tray freezing is a good way to stop the frozen raspberries from sticking together, it is not essential nor is it the only way. Provided you don’t mind the raspberries all clumping together, you can freeze them direct in a container, but you’ll have to accept that they freeze as a mass and you’ll need to “chisel” off clumps of frozen raspberries to use. Or, if you can fit them in a container the size of a standard lunchbox, you can mimic trays by using sheets of parchment paper or wax paper cut to fit the lunchbox-shaped container, and layer the raspberries that way, making sure they don’t touch. You can do several batches this way and transfer the frozen ones to a freezer bag afterward to keep them cold, then re-transfer the lot back to the container once all are frozen whole.