My experience matches Charles'. A pristine, freezer-weight, name-brand Ziplock will keep out the water and "vacuum pack" in the way your photo demonstrates. However, things don't stay pristine on my trips very long and a tiny knick by a tent peg, zipper or sharp pebble and the vacuum pack aspect goes away.
More substantial is the trash compactor bag, twisting the neck closed after blurring, and placed in a nylon stuff sack – that has served me well on canoe and kayak trips, but, you know, the boat floats* regardless of an extra few pounds.
I'm liking the Outdoor Products sil-nylon dry bags sold in a 3-pack. I've only got a year of use on them, and not a super busy outdoors year, but they've worked great, are lighter and quicker than the trash-compactor-stuff-sack combo and don't cost much at Walmart.
*except when it doesn't. I was on a boat that sunk in Cook Inlet last month (rather cold salt water) and most stuff was lost, and pretty much everything got very wet. But those drybags did their job for what was inside of them.
I was more impressed by my "Lifeproof" iPad case. When I went to retrieve my iPad off a beach 5 days later, it was still just fine.