Personal anecdote: my bread tolerance dropped dramatically on a 6 month keto stint. Sandwiches were gross there's just Soo much bread! Yuck! Then I got used to it again but now I stick with mostly rice/beans and have maintained my weight loss which is great
It's perhaps not as easy as a yes/no list, but 40% is very easy to figure out from the nutrition label:
max_carbs = calories x 1 g carbs / 10 calories
For example, a Sausage McMuffin w/Egg at McD is 480 calories, so as long as it has no more than 48 g of carbs, it's OK. (It has 28 g).
Make every item on your meal satisfy the 40% criteria, and the meal as a whole will.
Slightly up the effort scale, you can keep a running total of how much you are over or under for the day. Say you are going to get the Sausage McMuffin w/Egg for breakfast. That puts you 20 g of carb ahead. How about adding some McD Donut Sticks to the meal? 280 calories, 33 g of carb. That's 5 g too many carbs for the item to be 40%. But the McMuffin is putting you 20 g ahead, so losing 5 g won't mess up your overall meal. Go ahead and have those Donut Sticks if you like them.