I agree with some of the comments on the writing style. For myself it was more an issue with rhythm than length, but then I still remember the golden age of semicolons.
What you might try doing is reading the text aloud. See where you naturally pause for breath and adjust the text to accommodate. Use punctuation to guide the flow; that is probably more important than simply placing it where required.
I fell over backwards onto my pack while skiing down
Here each prepositional phrase adds to the tension (imagine a rubber band stretching). This might be a good time to allow it to relax rather than driving onward into "and I felt...."
Besides stream, lake or glacier water has no taste.
In this example I initially parse "besides stream" as the introductory phrase. A comma after "besides" fixes this:
"Besides, stream, lake, or glacier water has no taste."
If that's too many commas in close proximity, try:
"Besides, water from streams, lakes, or glaciers has no taste."
In terms of spellink and punctuation a simple re-read should catch most errors. Be aware your brain, in a sort of mental auto-correct, will still ignore some; allow a decent break before reviewing.
Here is another sentence that could use a bit of tidying:
How embarrassing – I was thinking to myself the entire time .Why did I bring all that extra clothing and gadgets?
A dash is actually quite appropriate here, but the flow feels off. Try:
How embarrassing – I was thinking to myself the entire time, "Why did I bring all that extra clothing and gadgets?"
"How embarrassing," I was thinking to myself the entire time. Why did I bring all that extra clothing and gadgets?