Toothpicks - Very useful during sculpting. There have been times when I had no access / could not locate my sculpting tool, so I turned to toothpicks. They're great, as you can cut and shape (limited) the wood to create the perfect tool for the job at hand.
Also, I use them when glueing two pieces of hard foam together; I stick a length in one side and after applying glue, I press the other side on top. Keeps the two parts from sliding out of alignment and they add strength as well.
And then they're great for a million of uses during terrain building; wood piles, campfires, wooden beams, fences, pallisades, litters, you name it; if there's a length of wooden pole involved in real life, you can use toothpicks for it in 28 (and even 15)mm...
Sanding paper - I've used this to clean sculpting tools, but also to create a concrete/tarmac/asphalt texture on my terrain pieces. Glue it down, spray it black and then paint and drybrush it into the desired colour. It loses much of its abbrasive nature that way, and the endresult looks really convincing...
Clothing pins - I have one in use that has been with me for over 10 years now; my trusty blueheaded pin... I use it for pretty much everything; drilling of gun barrels, opening of clogged paintbottles, marking/guide holeing drill spots, applying superglue or white glue in difficult spaces on miniatures, pressing holes in plasticard and many, many other applications I can't even remember...
Tape - The wide, crimping, paper packaging type. Not masking tape; packaging tape. I've used it to great effect to make tarps (over oil barrels for instance) and all matter of straps and belts on miniatures. Cut to the desired width and apply. It (sort of) sticks of its own, and with the application of some extra (super)glue, it's on there for the duration. It's thinner and more flexible than thin plasticard, which always has the tendency to return to its original shape. And a gun hanging from a belt that is bulging out sideways just looks daft...