there's tons of clubs both chapter based (linked to a national org) and interest clubs. not sure what you've seen, but in my opinion there are more chapter based clubs as opposed to interest groups. some of the chapter based ones would be SAOAO, AMWA, AWS, AANS, ACOOG, ACS, SOM, etc. you can see a full list here:
William Carey University College of Osteopathic Medicine Clubs. you'll have the opportunity to be more involved in E-Board of clubs second year. as far as first year opportunities, it's definitely worth joining clubs, and I know a lot of people in my year (who will be E-Board of your clubs next year) are working to have more opportunities for first years to be involved, do events, etc. There's also quite a few one off volunteer opportunities that will pop up from the school during the semester!
frankly as far as EC's go, beyond club events and the volunteer opportunities that pop up, you're just not gonna have time first year to do much else after you take care of yourself and your classes. your main goal first year should be to succeed in your classes; everything else comes second!
🙂