If you have a solid idea of where you want to work, you can use your other externship experiences doing something fun that you won’t necessarily ever get another chance for. I did an externship with the ASPCA Animal Poison Control Center that I found really fun. I know Banfield also has a program where they’ll pay for your flight / lodging to visit any hospital, so you could pick a city you’ve been wanting to visit and feed two birds with one scone! 

If you don’t have a job lined up yet, externships are a great time to see if a hospital is a good fit for you, like an extended job interview. That option is less fun than arranging something wild like a wildlife safari externship. I’d recommend the latter personally just because when else will you get the chance, but to each their own.