My car has a cup-holder that is too shallow; things fall out of it all the time.
This instructable offers a way to improve how a car's cup-holder and a way to reuse coffee house style disposable cups.
Step 1: Get Stuff
-a large disposable coffee cup
-a small disposable coffee cup
-disposable coffee cup sleeve
-glue of some sort
Step 2: Widen the Base
To help create a wider and thus more stable base, put the sleeve onto the large cup upside-down.
Flip both parts over (together) and try to get some glue into the space between the cup and sleeve.
Step 3: Base Ballast Bolts Become Bound Beneath Beverages
Toss some heavy stuff into the bottom of the bigger cup and cover it with a generous amount of glue. Let it dry.
Be sure not to overfill the big cup because you want the small cup to fit into it still.
If you use something other than washers and bolts for weight, be mindful of how you stick it in place.
Step 4: COFFEE CUPS, UNITE!
Once the glue over the bolts and washers (or other 'heavy stuff') has dried, drizzle glue all over the outside of the small cup and stick it into the big cup. Give it a twist to smear the glue around.
Step 5: Utilize
Put it in your cup-holder.
I had to rip the sleeve a little to get it into my cup-holder, but it's a snug fit and does what it's meant to do.