"How do people carry olive oil and butter?"
Because olive oil leaking is a true mess, and uncleanable on the trail, if the oil is inside my pack, I put it in a plastic bag, the bottle in a bag, that is. But I stopped carrying it inside my pack.
But now that I made a myog pack with nice big side pockets, I keep the olive oil in a regular 18 oz or so water bottle (like calistoga or trader joes bubbly water), you can get a rubber o-ring at the hardware store to make the seal at the cap even better if you are so inclined, o-ring goes around the bottle's top screw part, to make a rubber seal. Maybe not always best method, have to test it to make sure on your bottle.
I used to use nalgene 8oz bottles, maybe also 16oz, those have excellent closures, much better than regular water bottles, because they have an inside and outside lip/edge on the cap.
Or did, I don't know, but I always put the bottle in a plastic bag when packing it inside pack with food bag to be on the safe side, no issues.
Having the bottle outside I like better though, that way it's always pointed up, and you can easily see if it's dripped or leaking.
Butter, no thanks, olive oil is denser, and easier to pack, but if you must, then ghee type clarified butter is the way to go.
I doubt you can get any decent olive oil in a plastic mini pouch, that sounds not very appetizing, plus the taste of that plastic it's been stored in since packaging, no thanks.
So outside pack side pockets have water bottles, two, and one alcohol bottle and one olive oil bottle, that works well.
Lawson also sells some 8oz bottles, but those weigh about the same or more as the regular water bottle from the store, which is 18oz, ie, more than 2x bigger.
If reusing a water bottle, like calistoga, just make sure it's made out of thick / dense plastic, some are very thin, and will crease and crack over not too much time in a pack.
By the way, at trader joe's or whole foods you can buy 33 oz water bottles, called 'electrolyte enhanced water' that make great quart water bottles, they use thick plastic, and have round bottoms, and cost 99 cents each.