Very heavy traveling...the blue thing beow the side bag is a sun umbrella
Whereas I live the top case always installed on the bike, I put on the side bags only when I go for a long journey. The problem is that if the top case is enough if I am on my own, during the winter time, when I wear my motorbike jacket even when I gett off the bike, it is definitevely not enough during the summer, especially if I am traveling with my partner and we do not want to walk around with our gear on.
The main problem is where to leave our protective jackets, pants and shoes. In fact, I refuse to let my girlfriend ride on the bike in shorts and a t-shirt, even if it is only to go to the beach: we both wear our protective jackets and trousers and shoes. Obviously, as soon we get to the beach, we take off all this stuff, and we do not want to carry it with us.
Last year I bought for 75 Euros an anti-theft bag called "Stuffsafe", by Pacsafe. It is an 80lt foldable bag, which takes only a very limited space when folded. Unfolded, it can contain our trousers, our harmored jackets, our shoes, and whatever else you want...the textile is water repellent, and is protected by an exterior iron mesh which protects it from people who might try to cut the textile to steal your stuff. You can anchor the bag to your bike or to any other fixed installations, if you do not want to carry your stuff with you.
So far, it has proven invaluable: I fix it to the bike with the provided lock, and just head off to the beach...with peace of mind.