Over the years I've had lots of stuff in, on and behind a mini. Some of the more memorable ones...
In a van.... when we use to show Mutant, I could carry the whole display in the van in one trip. 7.5mtx4.5Mt vinyl floor, 24Mt of fencing, about 100 300mmx300mm mirror tiles, 4.8Mtrx1.8Mtr display wall (broke down into 12 600mmx1200mm sections), signage, banners, power supply, 4 crates of leads and lights, 2 crates of cleaning products, luggage for 4 people and a passenger (Jan carried the CD case in Mutant

)
In a sedan.... Too many to have any "largest load" stand out. The most challenging was probably with the passenger seat out, the father of the bride behind me and a bride with a large hooped dress and train - the challenge was keeping the bride clean
In and On a sedan.... a whole flat pack kitchen. Had about half the staff of the emporium of fine Scandinavian furniture (Ikea) out taking photos.
On a sedan.... Friend bought a new queen size bed (mattress, base, head and foot boards) but couldn't get it home - no problems ... just a few strange looks whenever you passed slower cars going down the freeway.
Behind a mini.... Once the son's crumpledoor broke down and he borrowed a triaxle trailer to get it home that had a foot of width to spare for the crummydoor. No I didn't pull the dunnydoor with the mini, but somehow the trailer got left at our place for a few weeks. One day I hooked it onto the mini to move it and thought that the weight wasn't too bad so took a test run around the block and then loaded it up for a tip run. Guy at the trip was laughing so hard he let me in for free provided he could get a photo for their wall.