If you have a front derailleur that's not shaped optimally for whatever sized large chainring you're using, a dremel tool can be used to reshape the derailleur cage. Example: I'm using a Shimano 105 FD with a 46t big ring, the FD is now shaped to fit the ring. Be aware, sparks do fly during the procedure (which is half the fun, really).
For real mountain biking (i.e. fat tires, relatively low air pressure), the approx. $60 it costs for a Stan's tubeless system kit is the best money you'll ever spend. That is, assuming you have conventional mtb rims and tires. If you've got a factory tubeless system already, whatever it costs for a container of Stan's sealant is the best money you'll ever spend-