Pre-university undergraduate IB related experience

Usually when you're putting your resume together to apply to Summer Analyst positions, you never include things you did in high school or before college. I would say if you haven't even started college yet, enjoy your summer. 

After your freshman year, over the summer going into your sophomore year, you could start looking for finance related roles. Maybe go to a local small brick & mortar bank in your town and try to connect with them to see if they can bring you onboard to assist in loan underwriting or some accounting tasks or something. My dad's college roommate became the head of retail banking for Bank Rhode Island (where I'm originally from) and he helped get me set up with an internship over the summer. 

The summer going into your Junior year is more important in my opinion. Maybe see if there are private wealth management firms near you and reach out them. "Hey my name is a blank, Im a rising Junior at Blank Univresity and I'm seeking to gain relevant work experience in the finance industry. Blah blah blah." Hopefully you can make a connection and have another solid internship. Also start networking for your Junior to Senior year summer analyst job.

Now during your Junior year, in the fall you want to get started with making your resume look sharp. You should now have some relevant course work, maybe a commercial banking/retail banking internship, maybe a wealth management internship, maybe you did some accounting help at a credit union or whatever. Hopefully your involved at your university as well.

Then get cracking at the recruitment process for a Summer Analyst position. Network everyday and make solid connections. Study for technicals and hopefully by December or earlier you'll have a Summer Analyst offer at a bulge bracket or elite boutique or wherever you wanna be.

Now during the summer between your Junior year and senior year, just crush it at your Summer Analyst gig and secure the full-time return offer. Then you can cruise through senior year and graduate knowing you're gonna be making good money. 

Hope this helps.