Don't left it to the vet, it won't like it.
Cats love to stay in their own environment more than being with company.
When we left up to 4 days, we left the cat alone with food for two days (because we feel guilty, but one day of food is enough, they don't eat that much when they are alone).
When it is more than 4 days (and it went up to 3 weeks), our neighbor/friend comes every other day to check on it and give it food and water. Since she feels guilty too, not coming too often, she stays a little and brings her kids to play with it. So the cat hangs out with them what it usually doesn't do.
The only things important to do is for it to get enough fresh water as much and often as possible (every two days is OK), get enough litter (if you don't want your neighbor to take care of that), and, last thing, close your bedroom doors in case of a doubtful revenge of the cat (just left him two-three rooms it likes to go to to sleep). My wife is allergic to my cat, and when alone, it usually went to sleep on (and sometimes in) my bed, so we had to close the door to avoid that.
You can also turn down the home temperature to about 60F, they are not as sensible as us on that.
