I've only eaten out once since on my Whole30 (this is my first)... we went to breakfast at Cracker Barrel and I had a harder time than I thought I would... They have NO veggie options during breakfast hours. I got a porkchop (no butter or oil) and the seasoning was very very light so I'm assuming that was good (hopefully), poached eggs... and a side of fruit (FYI - forego the side of fruit... it consisted of 2 small pieces of pineapple and 1 1/2 strawberries for like $2.59... no thanks). I've just decided to resist eating out for now, unless I absolutely have to.
To add to the Subway thought though, I definitely wouldn't resort to going there. Their meat is as fake as can be.
Actually, I did eat out one other time. We went to Outback Steakhouse - not fast, but a good option. You can get the steak that's woodfire grilled, and they have 2 options for the seasoning - I got the one that I think was salt & pepper only (can't find it on the website so I don't remember exactly what the menu says)... veggies, they have several options (green beans, mixed veggies, broccoli) you can also get steamed veggies with no butter/oil or seasoning. (beware of the grilled asparagus, I asked for no butter/oil, but there was something on it...)