At this point, I feel like it is pretty misleading to say Onshape isn’t a complete CAD option. Sure, there are still a few nice-to-have features missing, but stock Onshape would result in improved CAD for over 50% of teams. Add in MKCad, and I would bump that number up to 75-95% of teams. To be clear from a pure CAD prospective, I wouldn’t recommend Onshape (I use SolidWorks professionally). But for an FTC or FRC team, I think the advantages of the environment (collaboration, team and individual cloud storage, no installations, updates, or licensing) outweigh a handful of missing features (assembly mirror, exploded view, etc.). For all we know, these features won’t even be missing by kickoff. The barrier to entry is so low, every student on my team has an account and many of them use it to design, pull measurements, or just observe. This was unimaginable to me a few years ago before we switched.
But to answer the question at hand:
MKCad: pic: Introducing MKCad, the Onshape FRC Parts Library
I would also recommend my Custom Extrusion Featurescript detailed here: pic: Custom Length Extrusion - Onshape FeatureScript
That featurescript might appeal to building more complete structures in an Part Studio. I have added some configurable length extrusions to MKCad which is the other way to go about it. Each method has its pros and cons.
Most of these are now part of MKCad (just look for “Configurable” in the Document name): Vex Configurable Parts in Onshape!
Also: Some Helpful Featurescripts
Standard content for inserting hardware into assemblies (screws, washers, nuts) is built into Onshape now.
Some robots to reference: List of robots/mechs in onshape