So, my advice is to wear a good-quality daypack for the essentials (I assume you want the bulk of the load in the sled) and use its padded belt as the harness for the sled.

Harness. When pulling a weight sled, you’ll be doing so via straps and/or a harness. On some models, this is simply two straps that you need to grip in your hands the whole time.

The volunteers at the 2014 Banks BBQ tractor pull broke down the engineering of the sled into easy to understand functions. The modern tractor pull would not exist without the sled.