GPS receiver on a keychain
It's not the most sophisticated, but it beats having to carry a second handheld.
As the tech industry has finally come close to combining all major functions into single handheld devices (phone, camera, media player), GPS often remains the odd man out. But until that technology gets absorbed into uber-devices as well, there's at least one practical alternative: a GPS keychain.
It's obviously not the most sophisticated device of its kind, but Proporta's Freedom Keychain GPS SiRF III is "the world's most compact and neatest GPS receiver available," according to The Gadget Blog. The company says it can handle 20 satellite channels at a time for 10-hour stretches, connect with phones or PDAs by Bluetooth and works with all of today's major mapping software.
Depending on the size of your car remote, you may need to reinforce your pocket lining to handle the weight of your keys. But for $130, it's still better than having to carry around the dreaded second device.