>>2037839
frame bags are a decent solution. They are unobtrusive, the triangular space serves no purpose and storage is a sensible usage. It keeps weight central. The only things to keep in mind are cables and bottle cage locations.

Some handlebar bags are quite good, as long as they don't interfere with cockpit, hand position and cabling etc. Picrel is what i use for small items. It's attached to the stem and the bar, but is narrow so doesn't interfere with hand position. it has a transparent phone pouch on the top and is very easy to install and remove.
I also had a frame bag made to sit between top tube and bottle cages. That's a permanent fixture now, so handy.