Your package (purse, computer) is heavy. Usually it drags you down.
Do the Squirrel: Put your paws up in the center with the weight carried close to your chest or mid-section.
Now your sternum (breastbone) is more confidently up. Your tired shoulders do not go down unevenly.
And you can see better!
2. Do you put the seat belt around the heavy things?
Occasionally people are killed in a sudden-stop car accident by a flying object. Always secure your stuff.
3. I remind myself to open the passenger or back door and put my packages in nicely, rather than twisting over and hurling them from the driver's side...after asking people who have had back surgery, "What is the most important single thing you've learned, to avoid further lower back pain?"
4. When you go through a doorway increase your alertness.
Some examples: leaving the store - Thieves have a job and they study their targets, so look about. Leaving or entering buildings - possible ice or puddles, rugs, different walking surface, a roving puppy underfoot? A doorway at home can be painful if we rush...Doorway equals new alertness; now you're covered.
5. The Santa trick, three versions:
First, you can use a backpack or even drag a tarp to put the weight of your burden behind your back (the Fireman's Carry idea is putting the burden behind you to safely carry the most weight).
Second, think of Santa and get some elves. Ask for wimpy-weight shopping bags and use store helpers at that end. Can you hire someone? Etc. - you get the idea. Elves!
Finally, what else does Santa do? Relax with cookies and milk! Say, just imagine carrying fewer, lighter burdens (sorry - you still can't leave those electronics in the car! Another chorus of "Thieves have a job".) Or consider leaving that work instead of carrying it home. Another example: When I shovel, I make a large mug of green tea and work while it cools. Then the tea demands that I take a break in twenty minutes. My brain believes this, whereas I used to do too much at once. "Relax! Don't even carry so much!" is the final wacky tip.