Has a KLR rider I can put in my 3 cents worth.
Depends on how and where you ride for your brake pad life .if you do a lot of wet and dirt they go way quickly.. What kind of service life have you been getting . I suggest you install NEW pads before the trip and that you DO carry a spare set. If you are going to be on s very long trip through South America carry two sets of pads, they aren't very big and can stand the snide of being in the luggage . Pads are bike specific and can be hard to find at times. Carry a spare clutch cable , make sure the throttle cables are good and they will last .
Carry a spare tube for front AND BACK of correct sizes .
Know the fuses in the KLR and carry multiple spares ,.
Light bulbs can be bought everywhere so no need to carry , you shouldn't be riding in the dark anyway.
Have a fresh chain and sprockets and you will be good for Panama and back , if it's going to be a trip longer than your usual sprocket / chain life you could carry but those are heavy items to pack and can be sourced in Guatemala City as can new tires.
Has the doohickey been swapped out ?
Make sure everything is in good shape and adjusted to spec .
Other than tools and tire irons and patch kit and air pump you really don't need much more. Any part CAN break or wear out but it's impossible to carry all spares " just in case"

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93