I'm answering from personal experience, which although extensive, is of course limited: limited to black bears, limited to the Sierra and to the Rockies and to a lesser degree, Shenandoah, and limited to several long trips per year for 40 years, plus short trips, warm-up day trips and day hikes from our base camps.
We never carried a bear canister for day trips or even considered it. On day hikes, we carry trail mix, bread, cheese, chocolate -- the usual tasty assortment, mostly in a day hiker with, say, a box of raisins in our pockets. On the long trips, we have packs stuffed with food, tasty and freeze dried. No bear has ever approached us when we had our packs on, looking for food.
In our early days, before bear canisters were ubiqutous and in the era when hanging food was the norm, bears got into our food several times when we were camped. A bear can be very clever and determined in getting food down when it is hanging from a tree. And several times we were awakened by a bear trying to open a bear canister; they never succeeded.
We were never panhandled when hiking while eating, although I would draw the line at hiking with a dead rabbit or a large paper bag of blueberries dangling from my waist.
This is Ursus americanus only. We have no experience with grizzlies.