You need a backpack, exactly the tools you need for your car, and some tool rolls.
Or in lieu of rolls, box modules. I like Gearwrench for this sort of thing, like i texted you last night.
Grab a North Face Hot Shot or something, start putting tools in it.
Alright, this is just what i would do. Pretty much everything here i own or have used.
Wrenches: http://www.cripedistributing.com/catalog/product/view/id/7068/s/napa-7pc-full-polish-extra-long-pattern-combination-wrench-set-1/ (You'll need to find a 17mm for the Miata) Stuff in a wrench roll.
Double X extended pliers, they're awesome. You should have them. http://www.cripedistributing.com/catalog/product/view/id/5691/s/napa-p900-2pc-double-x-45-degree-pliers/
56 piece 1/4" socket set: http://www.cripedistributing.com/catalog/product/view/id/6826/s/napa-56-pc-1-4-socket-set-deep-shallow-90927-ro/ (easily small enough to fit in the backpack.)
Mini Pliers. You need these: http://www.cripedistributing.com/catalog/product/view/id/8037/s/gearwrench-82100-5-piece-mini-plier-set/
Long nosed pliers 6': http://www.cripedistributing.com/catalog/product/view/id/5730/s/gearwrench-6-long-nose-pliers-82085/
Slip joint pliers 6": http://www.cripedistributing.com/catalog/product/view/id/6293/s/gearwrench-82079-6-slip-joint-pliers/
Slip joint pliers 8": http://www.cripedistributing.com/catalog/product/view/id/5841/s/gearwrench-8-slip-joint-pliers-82080/
Long nosed pliers 8": http://www.cripedistributing.com/catalog/product/view/id/5607/s/gearwrench-8-long-nose-pliers-82086/
6" diagonal pliers: http://www.cripedistributing.com/catalog/product/view/id/6067/s/gearwrench-6-diagonal-pliers-82008/
8" linesman pliers: http://www.cripedistributing.com/catalog/product/view/id/6294/s/gearwrench-82089-8-linesman-pliers/
9" linesman pliers: http://www.cripedistributing.com/catalog/product/view/id/8764/s/gearwrench-82090-9-linesman-pliers-ro/
12" groove joint pliers: http://www.cripedistributing.com/catalog/product/view/id/5685/s/gearwrench-12-groove-joint-pliers-82094/
Vice Grips: http://www.cripedistributing.com/catalog/product/view/id/5648/s/gearwrench-82040-5-curved-jaw-locking-pliers/
Long nose vice grips: http://www.cripedistributing.com/catalog/product/view/id/8720/s/gearwrench-82043-6-long-nose-locking-pliers-ro/
Screwdrivers: http://www.cripedistributing.com/catalog/product/view/id/5550/s/gearwrench-10pc-slotted-phillips-screwdriver-set-82731/
3/8" socket/ratchet kit: http://www.tooltopia.com/gearwrench-80559.aspx
1/2" socket/ratchet kit: http://www.tooltopia.com/gearwrench-80709.aspx
Adjustable wrench: http://www.cripedistributing.com/catalog/product/view/id/6613/s/irwin-vise-grip-2078611-12-quick-adjustable-wrench/
Test light: http://www.cripedistributing.com/catalog/product/view/id/6260/s/kd-tools-24v-circuit-tester-3984/
I'm not done yet, just need to take a break lol.
Really just need a hammer, maybe a punch set, torque wrench or two, and a breaker bar.
You could slim down what you put in your backpack by getting socket rails and then just rolls from there, but if you're really just lugging the backpack out of the trunk to the track or garage, i'd just pack the E36 M3 out of it. All the blow mold ratchet/socket sets will fit in any decent sized backpack, and the rest can go in rolls. Maybe 30lbs total for the whole shebang.