You are correct but you missed out some of the worst culprits. A huge amount of methane is created by the fossil fuel industry and simply vented off into the atmosphere. This isn't our choice and the companies involved could easily take measures to stop this excessive release of gas but that would cost money. They don't do it because it hurts their already massive profits. When we fill up with gas at the station we don't have a choice to prevent this happening other than to boycott fossil fuels altogether.

Another culprit is the Big Ag business, where profit is used as the motive to produce beef as cheaply as possible. This results in the cattle being fed with methane producing foods that has been grown on cut down rain-forests. It's easy to blame the consumer but it is difficult to avoid in the regular supermarkets.

You are also right about excessive packaging but what is worse is the reluctance of food companies to adopt reusable or recyclable packaging. It has taken huge amounts of champagning and petitioning to get even the slightest change. Even then, with the slightest excuse they slip back into using the same old plastics, hoping no one will notice.