You may be right and it is maggots if he tends to eat dead things. If you still have the vomit, as others have suggested take that with you to the vet. You can also give them a nice description. Sometimes they will just go ahead and do a broad spectrum general dewormer and either check a fecal after treatment, or go ahead and check if there is a sample available and they know what they are treating for. Some dewormers work better for certain worms. Also if he will potty while on a leash give that a try after he has a meal to get a stool sample. If you take him with you to the vet, they try and get stool out, not very hard if there is any there. Most dogs do fine and don't mind too much. I wouldn't worry that you didn't go to the ER vet, it sounds like he is doing fine overall. We have waited several times before for the next day depending on what was going on, so I know how that goes.
Tapeworms can have small segments that look like grains of rice when dry, but usually if they are in vomit they are much larger. Assuming he is on monthly heartworm preventive, most have a dewormer also for several common intestinal parasites as well as heartworms. At the point most dogs would be vomiting up heart worms, you probably would have noticed a cough, decreased exercise, etc too (not always, but usually). Since you have been having fun looking at worm pictures you probably have a pretty good idea of what you may have at this point.
Have a fun talk with your vet when they open soon and hope you get a quick fix.