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Are they available to take 1 or 2 tubes, a phone, keys etc in relative safety without being big rattly crappy things off-road?
Ortlieb do saddle bags in various sizes https://www.evanscycles.com/ortlieb-saddle-bag-EV229699 I've the large which I use for commuting and is big enough for a mountain morph pump, a waterproof, t-shirt, socks, pants, phone, wallet and have room for a bit more.
I've not done any serious off-road with it but about a third of my commute is on a canal towpath and it copes with that no problem.
Topeak ones with straps work for me, Topeak ones with the quick release mount seem to be rattly things that break.
The Ortliebs are characteristically tough and waterproof but do suffer from being one large chamber so you can have some rattling if you have loose contents.
Try this one...
http://www.bigxtop.com/collections/cycling/products/mini-seatpack
Cracking little British company.
Thoroughly recommend them...
I have an Arkel one on the adventure bike and really rate it. It has a removable internal dry bag and compression straps
[url= http://www.arkel-od.com/en/seat-bag.html ]this one[/url]
There's a Lezyne one that appears to have a small pocket for phone/delicates, and a big one for tubes, tools etc. Are there any others that have this?
Ideally needs to carry phone, wallet, keys, two 29er tubes, puncture kit and small multi tool.