i usually keep all my unpaid parking tickets un my seat figure if im not going to pay them i might as well use them to hold my plugs and reg. right? ok just kidding i dont keep plugs under the seat
i take assortment of jets, fuel lines, oil, filters, wrenches and screw drivers, got some nice rope for towing i keep in my backpack, plugs, nothing major... iv been fortunate that i havent had much go wrong with my bike ....