I encourage current residents reading this to consider doing a fellowship that will add value to your career.
It's hard to see how a toxicology or wilderness medicine fellowship can augment ones pathway if the goal is community/fulltime clinical practice. Academic practices likely aren't hiring these in large quantity either. Many already have settled faculty for these positions and aren't looking to hire.
I do think ultrasound fellowship might add value still, but this is becoming saturated as well, and generally systems only need one ultrasound trained person for multiple sites. By the time that you choose and complete a fellowship (2-3 years from now) the game might be completely different.
Pediatrics might be a new avenue as some community sites look to build out pediatric programs, however the thought of being a PEM fellowship trained person and doing that as a career make me want to vomit (I say this as a father!)
CCM would be the best choice in my opinion. I think Birdstrike talks about his Pain fellowship, however that also seems like a stretch for many. It would be a complete career change rather than an augmented/dual practice. Also seems insanely competitive with how few applicants from EM that they take yearly. Consider that it will get even more competitive as EM people look for "a way out."
I personally think sports medicine is a dead end because of how much competition there is from midlevels, FM, ortho, and many other ancillary care providers.
Doing an administrative fellowship might be a hard pill to swallow, but if it gets you a job in a system or geography that you desire then that might make it worth it. Largely, however, these fellowships are administrative slave labor for a year without much added value to your CV if the goal is to go elsewhere.
I don't see how doing fellowship adds value for anyone going into community medicine. Why does a private group, or more likely, a CMG care if you did EMS/US/Tox etc? They make money when you see patients and order CT scans, not when you sit on hospital committees or travel to Africa to set up mosquito nets with your MPH from global health fellowship.
Toxicologists are one of the most highly coveted sub specialists within EM. Their fellowship is 2 years, so they are very few of them, and overall a hot commodity at pretty much every academic shop. As stated above, doesn't matter for community medicine, nobody cares.
EMS specific jobs are very hard to come by. Medical directors stay medical directors for decades, and there isn't a lot of turnover. Also, the pay from public service agencies is overall poor, so there isn't much academic buy down unless you have a really unicorn set up and a big time agency gig.
While CCM seems really appealing, I have talked to folks who have had issues. Midlevel creep in CCM is real (NPs/PAs intubating, putting in lines etc) with tele-ICU set ups is potentially going to be the model at a lot of places going forward. Also, the half and half gig in both the ED and ICU is very, very hard to find from what I'm told, however that may change in the future.
Wilderness medicine fellowship basically equates to "How to start a campfire using actual dollar bills" since you are pretty much burning a hole in your pocket for absolutely zero gain forward. The majority of academic programs don't even care about wilderness medicine.
Global health to me seems like a PR campaign for an academic shop. "Look we travel to impoverished countries wearing our white coats from our Ivy league EM departments". I know people do good things in the global health world, but in terms of the marketability for it, it doesn't seem like there's that much need.
Ultrasound may have some utility for a place that wants to set up a QA program where you can bill for images. There's still a lot of radiology turf battles. This is one of the few fellowships that translates a little better into the community environment.
Pain/sports/hyperbaric are super niche for EM docs, and I don't have a general sense of the marketability. Perhaps you get a better lifestyle, but I would assume it comes at some cost (namely that you have to do pain medicine, sorry Birdstrike).