I had the same concern as I went to work without my bar today and the only think the local shop sold that I could afford (I had 1.23p on me!) was a small cathedral city cheese snack bar) its 30g of cheddar. and 150kcal so I am assuming if I start to feel weak, rather than eat nothing until I get home from work at 6pm, the protein from the cheese may help me keep going. I dont want to mess up as I am within sight of my next goal and want to stay in ketosis and on track.