I have no experience with bike touring. I want to bike up the Saar River with my 13-year-old daughter. We are going to be doing a very slow-go of it, only 15-20 miles most days. I'm planning on leaving our big suitcases in Trier, and we will stop there for two nights in the middle of our trip, so we will have a chance to change clothes and so forth.

Anyway, for luggage my laptop we're looking at either panniers or something I can strap on top of the bike rack. I've seen some convertible backpacks that are just under maximum carry-on size (9.5 x 21.5 x 14 inches). This is too large to lay down on a bike rack long ways, but I wonder if I could just stand the pack up, so that the back of the pack would extend up over the seat.

Any thoughts? Is this a recipe for disaster? The important thing is that my bag be big enough for my laptop and some clothes. If I can use the right carry-on/backpack, I won't have to get another purpose-bought bag for the trip.

I've done short little tours with nothing but a backpack strapped to the back, but it wasn't ideal. You'll still want snacks in the bag and then they're a pain to get to. Maybe a milk crate may be a good option.

I wasn't keen on buying purpose build bags for a while either, but they do make life much easier. Where are you at? someone here may be willing to lend you some panniers for a short trip.

Trying to strap a bag to stand up in any stable way, that doesn't sound easy!

How about strapping it on horizontally, i.e. the longest dimension of the bag is parallel to the wheel axles, and the shortest dimension is vertical. The top and bottom of the bag will probably droop a bit, but that shouldn't really matter.

If you already have rear panniers, they are 'that' wide..

being clever my panniers, as special ordered. allowed me to cross brace rear rack top loads.

I've done the only reasonable thing. I've ordered a carry-on bag that I think will be suitable if perhaps a big large. It has a special slot for laptops.

I rode bikes a lot as a teen and young adult; actually took a 650-mile Europe tent trip with a van pulling the luggage. But I haven't ridden regularly in years. The town I live in reminds me of San Francisco when it comes to riding a bike. But, I'm going to buy a cheapo bike with a rack and try to get in shape a bit. I'll also try and see if the bag I've ordered can be made to fit on the rack. I figure peddling a few miles with a full bag strapped on will give me an idea of whether or not it will work.

It may sound dumb to plan a bike trip without having ridden much, but as planned our daily ride is only going to be about 15 miles. Not too taxing, I hope.