tubes
Your idea will work fine for Europe as shops and spare parts are readily available, but since you asked..
When I toured outback OZ with an IBEX trailer I had 2 spare tires for the bike and one for the trailer. I was using up tubes until I found out what the problem was with the rim tape - but, a home made "tape" made from a multi-perforated tube, and duct tape solved that problem. I started out with 3 MEC spares , but after it was all over maxed out at 5 tubes and used up one of them and one of the spares.... Eventually I sent 2 tubes back to Canada with a bunck of books, etc that I bought along the way.
I started out with 2 spare tubes and a spare tire for the IBEX and ended the trip the same way. The 2100 km route took 6 weeks (bitumen 1/3 and dirt 2/3)