Going back to the OP's question, "Any contenders?", if I owned a dog this thread could have been aimed at me!
Looking through my lists I see I saved 4.5g by buying a spinnaker fabric tent peg bag, 23g by swapping a plastic mug for a plastic measuring beaker, and so on. There are plenty more.
The top one has to be buying a little penknife for Ł7.99 to replace a Stanley disposable craft knife with the handle shortened, making a massive weight saving of - wait for it - half a gramme! Or should it be the perfectly good Braun battery shaver I've just replaced at great cost with a rechargable Wahl one that is 60g lighter? As it is discontinued I could only source one from Italy with a high postage rate.
I do add weight sometimes, though. For example a 17g rubber-and-plastic collapsible funnel for filling my water carrier is far more satisfactory than a homemade one cut from the top of a 500ml water bottle.