For on the bike I have no advice, for going on a plane...hardcases, hardcases and HARDCASES.
It's a game for us baggage handlers, to see how badly we can demolish your beautiful, leopard colored, corduroy shoulder bags. Never put anything breakable in there. If you HAVE to ship a bottle of wine or glass ornaments or some crap, wrap it 3 layers of bubblewrap, put several socks around it and then wrap a few tshirts around that.
Pack with the notion that the bag will be dropped from about 15 feet, multiple times, then have 3-10 heavy bags placed directly on top of it for hours. It will, if you're lucky.
If you pack your bags super heavy with everything in them, I and every other handler will make that extra special effort to run it over. 100 pound and heavier bags are just retarded, buy a second and third bag already.