Attending Camp Freightliner this week. They will be doing the Service on my rig while I am in class. I will be obtaining a set of spares to carry. I figure the things that are easily fixed IF you have the right parts are Filters and Belts. I will have a set. when i do the next service, we'll use them and I'll put new in storage. I already carry a tool kit, wire, fuses, tape, hose clamps and patch tape. It isn't like the old days an a naturally aspirated Chevy, you could fix just about any problem yourself and get home. I figure if I stall due to a clogged filter or I break a belt, having them shuold make the repair much more likely in a short time frame. If I have a major issue, nothing I carry is likely to help. That is where planned maintenance comes in. If you plan your maintenance and you follow through and DO your maintenance then the incidence of breakdown should diminish greatly.