Going from Oklahoma city to NYC, you aren't passing from a legal state to an illegal state, so there should be no border searchers, and those have to be pretty damn rare- there are a lot of buses leaving California, Oregon, Washington, Nevada, Colorado, and Massachusetts every day (i think those are all the states with rec weed stores?).
Also, riding Greyhound is so flaky, unreliable, and prone to stranding you for long periods when the connecting buses don't connect that riding without medications seems foolish. You will be glad you have it. I would not have enjoyed my unexpected 12 hour layovers in Pittsburgh and Grand Junction, Colo. nearly as much without my stash (Grand Junction is one of the few Colo. towns with no weed stores).
Also, earplugs are very useful on long bus rides, for when seated near screaming babies, loud talkers etc., or just to drown out the bus noise and sleep.