0.A SDL, Experimental 9b31058 (Windows 8.1)
I was playing as a new character (no ‘home base’ or vehicle set up to drop items in) with fairly low strength, and I only had a few pounds of carry weight left because the shelter I spawned in actually had some stuff in it. While looting a house, I picked up a plastic bottle of mayonnaise and was suddenly overencumbered by several pounds. Upon closer inspection, the bottle - which ‘holds 500ml of liquid’ - weighed 8.1 pounds. A quick google search reveals the density of mayonnaise to be around 0.03287 pounds/cubic inch, and 500ml is 30.5119 cubic inches, meaning the mayonnaise itself should have weighed (0.03287 * 30.5119) around 1 pound. Also, by comparison, a gallon jug of vinegar weighs 8.8 pounds (this is much more accurate).
Either that plastic bottle weighed 7 pounds by itself or this is a bug.
Weights for most bottled items seem to be very inaccurate. A plastic bottle of mustard is 5.61lbs, a plastic bottle of honey is 5.6lbs; plastic bottles of water and salt water are actually just over half the right weight at 0.6lbs (500ml of water weighs 500g; 500g is around a pound, not half a pound.)