The only physical thing I can see worth sending would be Von Neumann probes [0], essentially nanobots that could build things including more nanobots.

To get to the highest velocity you need a very low mass fraction. You need your ship to be mostly propellant. All the mission equipment would be constructed at the destination out of ship structures and raw materials at the destination.

If you've got nanobots that can directly construct anything you want you live in a post-scarcity Soviet so economics aren't terribly meaningful anymore.

[0] https://en.m.wikipedia.org/wiki/Self-replicating_spacecraft#...