What are some recommended summer activities that I can do over the summer to show my interest in the Pharmaceutical Sciences field?

Look for internship opportunities at research labs in a university or college near you. Some schools let high schoolers come and observe for a few weeks and sometime you can even put together a little project and work in the lab under the supervision of one of the junior scientists. This will give you some exposure to the field so you know if you really like it.

Since you are still in high school, I believe in high school there is job shadowing in high school that you could participate in, the best source for that should be your advisor st school, ask her if your school offer these. Also, you can find cashier jobs in a pharmacy if you want to learn about it, as far as other pharmaceutical related job, you can try to google out the company human resource department, tell them that you are high school student and looking for opportunities to shadow someone in the filed ( with your parents consent of course) as them if their company offer such thing for students, I know lots of company does, as for other medical professional, you can ask to be volunteer at hospital then use the opportunity to ask to shadow doctor/pharmacist etc. good luck!

See if a local independent pharmacy will allow you to observe particularly if they do extemporaneous compounding.

Science isn't my field, but I was just thinking that you could start searching for online courses online, like pre-college preparation. Try Coursera and edX.