I feel like the backpack makes me hot. I strap my backpack to my front porteur rack or rear rack. I also have a pannier basket that fits most of my backpacks that is a good option.

I also go a panner style messenger bag (with hooks). This is a decent option. Not perfect for me, because the messenger isn't my every day bag and doesn't match my own personal style. I recently got pannier that I have used a luggage lock to attach to my rack for security. But I am not leaving them on my bike for more than a few hours.

I have a work backpack and a purse. These currently go to my porteur rack. I take this with me.

I can see why people like the Ortlieb bags, but they aren't practical for me all day!