I use a digital food scale. Simple and quick, grams, ounces, whatever you tell it. Zero's out on reset with food still on it, making additions a snap. Salad: add broccoli, write down the weight, zero it, add radish, etc etc. Makes it great for weighing small amounts, like salad dressings, lite grated cheese, croutons...
Almost all food labels have serving weights in grams. If not, simple conversions tell what fluid ounces converts to, and even simpler, 1ml = 1gram for most liquids.
(it's defined by water, 1ml water = 1 gram)
One thing to be wary of is some volumes don't convert to the stated grams. For instance, the Quaker Old Fashioned Oatmeal label says 1 serving = x grams, and it doesn't. I called them and they said to use the volume measure, so I just break out the measuring cup.