It's nice, and saves a lot of math, to get a digital postal scale that has a "tare" function. That means you can weigh large or fluffy items that need to be on a tray or held down by something without having to subtract the tray (I use a cookie sheet) or whatever I hold the fluffy item down with.
Mine is a postage scale, Pelouze, weighs to nearest 0.1 ounce or 1.0 grams, has a tare function, maximum weight 5 lbs. (I hope nobody has a single item weighing more than that!). It was $25 when I got it at Office Depot but like everything else the price has gone up since 2006.
Of course, such a scale (like all good backpacking gear) has multiple uses. If you cook from European recipes (they weigh ingredients instead of measuring) it's absolutely essential (and, IMHO, more accurate for baking, especially measuring flour). It can, of course, be used to measure postage. That's how I check my scale's accuracy every spring just before April 15--weigh tax returns on mine and then at the PO. Dieters find an accurate scale useful for weighing portions.
My scale is small enough that I can cram it in my purse when shopping. The clerks at REI give me a lot of dirty looks as I go through weighing items and putting them back on the shelves. I never trust manufacturers' weights--the "cottage" manufacturers are pretty good about accurate weights, but most of the big-time manufacturers consistently understate their weights. I have several times returned items that weighed 4-8 ounces more than advertised!
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey