Pop popcorn in an air popper or on the stovetop. I prefer an air popper - it produces perfect popcorn every time without burning it! Pick out any unpopped kernels. Place popped popcorn in a large brown paper grocery bag.
Place butter in a microwave safe bowl. Heat on high power for about 30-45 seconds until butter is melted. Add sugar, stir, and heat an additional 30 seconds. Stir, then heat again for 30 seconds. The mixture should slightly boil. If not, heat an additional 15-30 seconds but be careful - it can burn fast. Once it browns it's gone too far.
Stir butter and sugar mixture to make sure sugar is mostly (if not all the way) dissolved. Add salt and stir. Pour butter mixture over the popcorn in the bag. Close the bag by rolling it down and shake it several times to coat the popcorn. Let it cool before making the mix.
To make the mix: place popcorn, almonds, pretzels, and M&Ms in large ziploc bags. Seal and eat within 3 days. Optional: add other crackers or candies or raisins for a variety of snack mix flavor. The beauty of this recipe is you can make it how you like it.