While most speedster owners complain about having too much free storage space in their cars, I found myself in a totally different situation. Because I like to carry a spare valve cap for one of my tires, I ran out of space.
What to do? Here's an approach that I trialed this morning with decent success that I'll share for comments and criticism. I tried using the mostly empty space inside the doors (the space that spyder owners take for granted).
My car: I've got @Vintage Motorcars Inc leather interior door cards. The cards themselves are made of a nice flexible 1/8" plastic. The leather is glued to the card and then stapled around the edges on the inside.
My approach: First remove the door card and mark a line across the back where the card will bend upwards. Wait, there's something you need to do right now. Go back to the car door and strike it with your palm a few times listening for rattles from the door handle linkage. Apply bits of foam around rattling parts as needed. Ok, back to business.
Figure out how deep you should cut and put a spacer on a dremel cutting wheel that lets you know that you are cutting the correct depth:
Not too deep!
Cut across both sides until you reach where the vinyl/leather is folded around. I found it was easier if I cut from the right hand side to the left hand side.
Using a screwdriver lift the edges of the covering away from the card. Remove staples as needed and save them for reinsertion.
Loosen the covering around the side and front of the card directly underneath where you will be extending the cut and keep the blade of the screwdriver beneath the cutting area so you won't accidently cut the covering at the edge.
Gently flex the card so it folds upward in the middle of the panel. Correct any binding cut areas.
Using rubber cement or upholstery cement, glue the covering back down and restaple it. Pro tip: buy a cheap bag of disposable acid flux brushes to use to apply cement and to do touch up work. Then just throw away the brush.
Find the roll of velcro strips that you bought 40 years ago to make binders to keep your trousers out of the bicycle chain while you riding to work. When you can't find it, go to Lowes and pick up another roll.
Even if the velcro has a sticky side, use rubber cement to attach it around the sides and bottom of the piece that will swing up.
Reattach the door card at the top of the door. Then mark the areas that will need the matching velcro pieces, treat everything with rubber cement and attach. 
Voilà
Space for that extra tire valve cap, your extra large bottle of ketchup and the big stillson wrench (although not as big as @DannyP's or @Gordon Nichols'
And, it folds back down to be secured with the velcro strips hiding your ketchupy treasures from the casual observers (take that spyder owners).
Ok, I only did one and it took me nearly 2 hours. I'll probably do the passenger door at some point. I'm thinking I'll swap out my rolled up tool bag for the ketchup and stillson freeing more floor space in the frunk. There's probably room for some of my standard spares like belts, cables too.
Alright brain trust, what do you think? Anything that needs to be done better?
(great thinking outside the box Mike!)
