Either pb&j with some form of vegetable or leftovers in tupperware, rubber-banded shut and kept as stable as possible in the luggage (be it pannier, trunk bag, or backpack). But my commute is only 40min.
For yours, definitely icepacks and an insulated bag of some sort. They make them about traditional lunch-bag size, so it wouldn't take up too much room.
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--Ben
2006 Trek SU100, 2009 Motobecane Fantom CX, 2011 Motobecane Fantom Cross Uno, and a Bakfiets
Previously: 2000 Trek 4500 (2000-2003), 2003 Novara Randonee (2003-2006), 2003 Giant Rainier (2003-2008), 2005 Xootr Swift (2005-2007), 2007 Nashbar 1x9 (2007-2011), 2011 Windsor Shetland (2011-2014), 2008 Citizen Folder (2015)
Non-Bike hardware: MX Linux / BunsenLabs Linux / Raspbian / Mac OS 10.6 / Android 7