Fasmov Silicone Collapsible Storage Bowls with Lids-Set of 3
You can never have enough kitchen storage. These collapse down and take up very little space when not in use.
Get lots of fuses, you'll need them. Note that some campers may also use inline fuses (the glass tube ones) in some areas so you would want those as well. My camper has one for the slide and is behind where the battery sits so make sure you know what you need before you go.
You're going to want a number of bins in different sizes to keep things organized and ease packing and unpacking. I prefer clear ones so I know what's in them at a glance but that's just personal preference.