There are 2 things that are considered as a big plus in your CV during your residency interview .High Usmle score and USA clinical experience.
So try to have as high score as possible.
Regarding clinical experience the only relevant one is doing clinical elective rotation in some of the US med schools. That is possible to do only while you are still in your med school. But requirement for that is to pass USMLE step 1.So I am afraid that you will not manage to do that having in mind that you will finish your med school next year.
Observership is done by med school graduates and you are basically a shadow of a doctor and you are not allowed to touch the patient. This will not be valuable at all during interview - they might not even consider it for a clinical experience.Research is basically nothing - just wasting your time.
So finish your med school and give all the steps and you will be fine.
You are already superior to many applicants for residency because you are US permanent resident.
Good luck