I brought tuna for a sandwich to work one day. I realized that I had no can opener, but I have diagonal cutters, though. After I destroyed the top of the can, I needed the magnet to extract tiny bits of metal from the tuna. Not a good idea.
A can opener now lives in my tool box.
You should always pack your own lunch. It will save you a ton of money and time, as well as allowing you to buy better quality ingredients in bulk. I used to have a "snack drawer" in my tool box. Now, I have upgraded to a "mini fridge" :-)
Trust me on the can opener.