WolframAlpha is pretty good for calculating all this automatically—probably much faster than the spreadsheet. For example:
http://www.wolframalpha.com/input/?i=1+cup+milk+%2B+8+oz+yogurt+%2B+1+banana+%2B+1+slice+bread+%2B+1+slice+cheese
I used wolfram-alpha to get the nutrition information for a banana, but for everything else I have a much more accurate information. However, you are right that using wolfram-alpha can give you a much faster (although rougher) estimate.
WolframAlpha is pretty good for calculating all this automatically—probably much faster than the spreadsheet. For example:
http://www.wolframalpha.com/input/?i=1+cup+milk+%2B+8+oz+yogurt+%2B+1+banana+%2B+1+slice+bread+%2B+1+slice+cheese
I used wolfram-alpha to get the nutrition information for a banana, but for everything else I have a much more accurate information. However, you are right that using wolfram-alpha can give you a much faster (although rougher) estimate.