From my point of view and since Uncle Bob (I came up with that name...) is a dear friend my recommendations are going to be things that are not commonly found elsewhere, in demand, and as such represent an opportunity for RC Tonewoods to make some money while also providing a valuable service to us.
1) Grobet nut slot files - these are very hard to find these days but still very desirable
2) Glue-Boost products, OLFer Rick Rosenberg. We like this stuff a lot but you can't get it very many places. Jescar has it but how often do folks order fret wire. It would nice for Bob's clients to be able to pick up very high quality and uber fresh CA while ordering that set of Cuban Hog!
3) Jescar fret wire which is what I believe to be the best stuff available.
I'd avoid bone because you and I both know how often we read on this forum that folks are buying on price.... not necessarily quality and that makes bone to many a commodity which will always be sold on price to many.
I'd also avoid pick-ups because there are so very many choices now, everyone wants something different, and pups are commodities on the street as well often purchased from an Internet reseller also on price. The same is true in my book for tuners - commodity sold on price only and widely available.
4) Quality, prepackaged HHG. Although available at a few others a wood seller should take advantage of being a "one-stop" for many of the consumables that we all know we need when building.
5) Bridge pins but what the others mentioned can be had now. What's very hard to find is 3 degree, unslotted pins which is our first choice in our efforts to reverse the devolution of the bridge pin since the advent of cheap, moulded plastic pins. 3 degree ebony and rosewood unslotted pins would be very desirable and the last batch that I bought I had to have custom made they are so very hard to find.
6) Get with Murray McCloud he's a member and see if you can resell his excellent fret leveling beams. This is the way to go in our view, leveling beams, and how we teach to level frets as well.
7) I didn't talk to Andy about this but Andy Birko makes excellent faux bound CNC fret boards but I don't believe he has a distributor or reseller. I can see these being available in standard scale lengths and "off the shelf" as a real boon for anyone needing them (I used them on my stuff but from J. Watkins since Andy was not in biz yet). This makes RCT a one-stop again with not only the tone wood available but fret wire, pins, CNC boards, glue, etc. all taking their place in that big box that someone is looking to receive.
Kind of reminds me of saying would you like fries with that...
Hope that something here helps Uncle Bob!