Alrocket

My current Sette (from Pricepoint) is flopping all over the place when I'm on the trail. It's also pretty small, with kit, levers and multitool I'd be pushed to fit a tube in there too.

So can I ask what you guys are using? I know there's a lot of camelbak fans here... I like my back free, prefer to carry water & tools on the bike

I'm looking for something that is ...

• secure. Really, really secure. Both that it won't fall off the saddle, and also that it won't accidentally open spilling my stuff all over the trail.
  
• non floppy. Might come under the above, don't want the bugger hanging out to the side banging into my leg and convincing me that it's going to fall off any minute.
  
• about 1 litre size - don't mind plus or minus a little bit, but it's nice to have space for arm warmers, hipflask and a pack of gummi bears!
  
• waterproofing would be nice, but not a must-have.

I did see an ortlieb one that was a roll-up sealed for security and waterproofing, pretty nice. Any thoughts?

Edit: link to Ortieb one.