South America Tips

I am getting ready to set off on a South America backpacking trip beginning in October and ending around Christmas time. I am planning to hit Colombia, Ecuador, Bolivia, Chile and Argentina. The itinerary will include a mix of hiking, city exploring, scuba diving, and beach relaxing.

Was wondering if anyone had any tips in terms of: 1. Underrated / must hit places 2. Packing items found to be particularly helpful 3. Any safety tips 4. Anything else that is thought to be helpful!

Thank you in advance - any advice is appreciated!