Most useful trailering accessory you've bought?

[Catchlight]

Our build list is now etched onto a stone tablet in Kim's office, and we will pick up our trailer exactly two months from today.

Now that we have carefully researched and selected our Escape-supplied options, our thoughts are turning to outfitting the trailer for travel and camping.

We have two questions for the experienced campers on this forum:

1. What is the most useful accessory you've bought for your trailer from a source other than Escape? It could be a safety item, something to help with hitching or levelling the trailer, an entertainment source, or a kitchen aid -- anything that continues to enhance your towing or camping experience.

2. Where did you buy that item, and what are your favourite sources of trailer accessories in Canada, in the Northwest USA, or online?

Thanks for any suggestions.