I own several lunch coolers and use them constantly. I use them for both lugging food to work or other engagements (like roadtrips, picnics etc) and for keeping frozen items cold when going to the store for a quick fill-up trip on my way back home from work.
We have a fridge and a freezer at work so I usually don't have to leave my food in the cooler for longer periods of time but I prefer to be safe with my food and use a cooler even though my walk to work is less than 30 mins.
My favorite for the last half year I've owned her has been a
HM beige cooler which is actually the best one I own - keeps my lunch cold the longest. It's also a nice, understated look and it fits into my larger tote bags.
Another favorite I use a lot is a
Built NY Getaway Lunch bag which is neoprene. They have single colors and different patterns, I love the beige&white striped one from the new collection!
Both of these can fit a small tub of yogurt (=breakfast as I don't eat brekkie at home before work), lunch container and a snack. With the right choice of containers, I can usually fit a small thermos with my morning iced coffee in there as well.
Kate Spade and Day Et also do pretty coolers. I own one from Day Et and it's one of the larger ones that can actually fit a picnic lunch for 2-3 people but they do smaller ones as well.
What I've found is that many brands that do baby supplies also do small coolers - and with the beige mom trend, they often do light colors, beige, grey etc.