It pays better than being a hospital dietitian in Austin
Don't get all certifications. Just get the good ones: ACSM is the research/academia valued one, NASM is the one that gyms want you to have and is very good (probably better than ACSM and also has research), NSCA's CSCS is also good if you plan to work with active people or in collegiate/professional sports. The PES/CES are ok, ISSA is meh, and the Cooper Institute is respected but not national (it's a Texas one I believe).
Stay within your scope of practice. You aren't trained as a nutritionist or dietitian, so don't make shit up. You are also not a physical therapist, occupational therapist, or doctor. All of these, including the RD, require way more school than the cert did.
Having kinesiology degrees, the fact they make me get a certification is insulting. There's quite a difference in the education level between someone who learned stuff online in 2 weeks and someone who has studied it for years in an academic setting, with quizzes, tests, projects, practicums, internships, social aspects...