With summer winding down and fall just around the corner, now is the perfect time to squeeze in those last-minute adventures before back to school season kicks into gear. If you're looking for some apparel to help you seamlessly transition between season and prepare you for the great outdoors, look no further than REI. The retailer is currently hosting an end of summer sale with up to 50% off brands like Patagonia, On, Arc'teryx and The North Fa…