Three weeks is a long time to be expected to pooper scoop for a neighbor - a gift certificate to a restaurant and a bottle of good bubbly or wine would be appropriate. Just make certain the neighbor drinks first - don't give alcohol to someone who doesn't imbibe.

Also make certain the neighbor knows who your vet is, leave the kitty carrier where it can easily be found, and your contact phone numbers.

Can you take your cat with you?