When I have seen people using bikepacking gear with no racks on the bike, that often meant that they put their luggage anywhere they could and ended up wearing a small backpack for water and other overflow stuff that did not fit on the bike. Or, they put a bladder of water in the frame bag. Some people appear to not mind wearing a backpack while on a bike, I prefer all my weight on the bike instead of on my body.

But I am seeing more bottle cages on front forks too.

I prefer water bottles, I know how many bottles I have used and how many I still have full. If I had a big bladder of water, I would have no clue how much remains.

Sometimes I use the one liter Smartwater or Life WTR brand water bottles instead of bike water bottles, although they are intended to be disposable they work well in a standard water bottle cage. But if mounted below a downtube, it is best to use a piece of velcro or elastic to hold it to the downtube. Only their one liter size fit cages, but occasionally I see a different brand that has a smaller bottle that also fits cages well.

One advantage of these disposable bottles is that they are less likely to leak and get your other stuff wet if in a pannier than standard bike water bottles. If I am in a hot weather environment, I might carry extra bottles of water in a pannier or rack top bag.

Some frames you can put a full liter under the downtube, but most bikes you can only put a smaller bottle down there.