You ever get nicotine poisoning? That’s a good example of strong cholinergic effects.
For a direct cholinergic agonist, may I suggest
epibatidine, a potent chlorinated natural product that was recently in the news for its use as a poison by Putin. This compound is strongly analgesic, and drug companies tried to develop it back in the day into something that was less toxic, to make a non-opioid analgesic. No analog developed ever had mild enough side effects to get approved.
Or maybe you wanna get more nonselective and into the realm of acetylcholinesterase inhibitors. Then you get some of the really nasty stuff like
EA-4056, a carbamate nerve gas that is 3 times more potent than VX.
For actually taking, I’d echo TheLightBringer and say best bets are things like nicotine or arecoline or very weak acetylcholinesterase inhibitors.