Josh has some good stuff up there.
I opened for years with asking for someone to name a card, freely--no forcing--then reaching into a pocket with no hesitation and two fingers and pulling out the named card. I used a 4 card per pocket (8 for the big jacket pockets) that let me keep all of the essential cards plus some outliers. If you do the research that Josh suggests you will find out that it is a rare spectator that will name something truly random like the five of spades. We are talking lay people here. They will name an ace, a court card, a seven, a two pretty much in that order of probability. In the rare event that they named something I didn't have I just did an invisible deck routine.
As far as having a spectator reach into your pocket, unless you are wearing a jacket that may introduce an unwanted creep-factor. For my trick I don't think it would have added anything worth the extra work since it was my opener.
There are some good pocket index systems in old books, unfortunately most of them were designed for jacket styles that were much more generous in the pocket department than modern fashion.