Sanford Sharpie Industrial Markers
Regular sharpies are great, but industrial sharpies are the best thing ever. They aren't soluble in ethanol, they take longer to wash off of skin, and deal well with extreme temperature. I constantly walk around with one or more of these in my back pocket, probably making people nervous that I'm going to start tagging at any moment. I use these in lab to label things that are going to be sprayed with 70% ethanol (great for tissue culture), or are going into the liquid nitrogen freezer, or high use items that would get their labels rubbed off easily. At home you can use them to label just about anything, or draw something cool, or go ahead and tag if you want. Just be careful because the only thing that removes their ink really well is acetone (nail polish remover) and that will melt some kinds of plastic.