Does it have to be leather? If not, and you are looking for a travel bag that you really don't have to worry about, then check out the Paris-Biarritz line. They are coated canvas and have a zip top. They are also big and roomy and are marketed as travel bags. Otherwise, the cabas is such a wonderful bag and I wear mine A LOT.
I think either a Baby Cabas (the smaller size, which ain't exactly "baby" haha) or a Diamond Stitch tote would be perfect! I have a Khaki Baby Cabas and it's a great slouchy bag you can just throw over your shoulder and go without giving it a second though... like DD101 said, the fact that it just has just a snap closure could be an issue, but it molds to your body when you carry it and has a zippered pouch inside, both of which ease my worry about someone running off with my stuff!
The Diamond Stitch tote has really great, durable leather and comes in two sizes (check out the Reference Library ), and that tote has a zipper that goes all the way around, which is great! Btw, I lurk in the HIA thread (no Hermes for me hehe, only a belt and some Twilly's... I'm a Chanel girl at heart ), but I have to say, you always look gorgeous in your pics!!
It sounds like you want something less structured that you can toss a bunch of things in when on the go so I'll skip the GST.
The modern chain is my everyday tote but it is a bit heavy..comparable to my 40cm birkin really but more useful because I can carry it on my shoulder. It is also lined in leather which you are used to with the Birkins and is my preferred lining.
The Cabas bags (original and baby) are lined in canvas if that matters to you. The baby cabas has had many complaints about stitching coming loose around the quilting area on the bottom I think. I had the original cabas bag that you posted before selling it as the modern chain was better for my needs. I paid $1850 for the original cabas which was the original price so keep that in mind when buying on ebay with the high markups some put on this one as it is sold out in stores. Ebay and consignment sites like Anns Fabulous Finds have authentic ones listed occasionally. There is also the Brooklyn Cabas that has patent leather and lambskin.
There is another tote that is currently in stores that I can't think of the name of that has the CC in silver hardware and has that quilted silver interior lining and short handles. Anyone know the name of this? Boardie Addisonshopper tried it on and loved it at our DC area meet and greet. You might ask her.
This may be out of context, but I adore every single handbag I have and I worry about them when I travel. In other words, I only travel with my Prada messanger. It's amazing, doesn't scratch, wipes off very well, and it still has character. I pack beautiful clutch's for dinner(actually 1 so that I could buy others). Funny thing is, when I travel, the things I miss most, are my darling handbags and my jewelry.
I love the Outdoor Ligne. It is distressed caviar leather and wears like iron. I take this blue HOBO bag with me on all trips and whenever I have to fit a ton of stuff in my bag. It is not a structured bag so if you are not used to that you might not like it. But for wearability and travel you can't beat it!
But here's an idea of the size compared to my MC tote: