Normally I'd say, "I brought my lunch" or "I packed a lunch". To me, a "boxed lunch" is something you buy premade at the deli or grocery store. No one uses the expression "sack(ed) lunch in Canada. Some people use the expression, "I'm (brown) bagging it this week", which means they are planning to bring their own lunch from home.

In my opinion, Any of these could also be provided by a company. These are just describing the way the lunch is packed.we commonly used these words to describe a business lunch for example. To be clear just say I brought my lunch from home or I packed my lunch at home.

Packed lunch - you say this for any lunch that you make at home (even if it isn't just a sandwich), it could be a Tupperware box with pasta in it, or an Egg salad in a bowl. It could be any food, it just comes from home - not shop bought

All are fine. My wife used to say to me "have you packed your lunch?" And, as mentioned by Naomi, it common to use the phrase "I'm brown-bagging it today." Always "brown-bagging." The reference is to a paper bag, made of a kind of tough, cheap paper sometimes called "Kraft paper." The "bag versus sack" thing is interesting. I haven't heard the phrase "sack lunch," but that's because the use of the words "paper bag" and "paper sack" are regional. Everybody understands both words. If I hear "paper sack" I don't think "what is that?" I think "she's not from around here" or "Oh, that's what Aunt Karen from Iowa used to say." Here's a map showing the regional use of "bag" and "sack:" https://www4.uwm.edu/FLL/linguistics/dialect/staticmaps/q_109.html

In the UK we say packed lunch. You could say I've brought my lunch or I've brought a packed lunch. We don't normally use phrases like "brown bagging it" in the UK. (I suppose its because the brown bags Dan mentiined above are not as popular here.) Generally we wouldn't use box lunch, boxed lunch or sack lunch either. However a lunch box or lunch bag can be used to describe the container for your lunch.