You know, over the years there have been numerous accounts of what people do and don't put on their sticks and why.  While there probablyu aren't any hard and fast rules, (at least not that I am aware of) there are probably a couple common sense guidelines that could be assembled regarding this very topic. Thinking back over all the different combinations it occurs to me that if we were going to have a rule #1 for what should or shouldn't be on the stick, for my way of thinking it would be this....

Anything that is flight critical, or that by its operation or failure could ultimately result in an in-flight horror story, should never be incorporated into the stick grip.  This includes flaps, landing gear, propeller pitch and speed brakes.

So why are the trims typically included?  In general, the trims are typically able to be overcome by the normal flight controls, or they can be easily disabled by pulling their breakers in the case of a runaway.  They also tend to be slow operating and the PIC can usually tell when one is going beyond the limits he feels comfortable with.

I would have included the starter in rule #1 but I think it is better covered by rule #2...

Any switch that is actuated only once or twice per flight should not be incorporated into the stick grip.

Here you have the starter, landing and taxi lights, nav lights, strobes, etc.  This brings us to rule #3

Save the buttons and switches on the stick grip for things that are accessed frequently and assist with managing pilot workload. 

This obviously includes the trims, push-to-talk, auto-pilot disconnect and control-wheel steering.  Other appropriate items might include comm frequency flip-flops, EFIS screen swaps, and in the case of engine monitors with multi-page displays, a paging switch for them.  There was discussion sometime ago about incorporating the squawk into the stick, but the concensus at the time was that since squawks usually are accompanied by a squawk code change, your hand is already near the transponder, so the squawk button is readily available.  You also don't want to squawk inadvertently... bad form.  Reaching for the squawk is a good thing.

Well, there you have it.  I don't know if there's an actual regulation or mention in AC43-13 regarding what should or shouldn't be on the sticks, but these 3 easy-to-remember rules seem to make a lot of sense.  Of course, this is only my opinion derived from keeping my eyes and ears open over the years, so I welcome alternative viewpoints.

   <Marv>