Rebuilding Ukraine’s army is an expensive undertaking and the country doesn’t have the cash to do it.
All it can hope is the Russians will calculate an invasion is too expensive for them.
We should send them some stuff—maybe some old things we have. Give them some old mothballed ships. Like Lend Lease in ww II—Maybe we could send some hot fighters and pilots like the old Flying Tigers in China ? Europe can help with some arms. Russians may want a land link to Criema. The US should give them some planes and ships. Better them than the Moslem Brotherhood in Egypt.
There are numerous things Ukraine can do though, in the event of a major Russian military push. They can start getting the roadside bombs ready. I remember in Iraq, the insurgents managed to stop entire convoys of trucks and even heavy tanks by merely putting suspicious looking devices on the side of major roadways. Snipers are also effective. The Ukrainian military can get out of their uniforms and go full blown insurgent mode. That with funneled in surface to air missiles and other assorted nasty surprises we learned the hard way to deal with in Iraq and Afghanistan, the Russian military can once again be forced to reevaluate what they are doing like the Mujaheddin forced them to do at earlier point in Russian military history.