Normal road leisure / training / club ride:
-Gilet, midweight rain jacket, phone+cash+card, banana or two all in my back 3 gilet pockets.
-1/2 inner tubes, multitool, quick link, 2 tyre levers, a spoke key and either by headlamp battery pack or some road cleat covers all in a medium wedge saddle bag.
-2 bottles 500 or 750ml depending on speed/weather. One with water and one with electrolyte or energy stuff.
MTB:
Little 13L Osprey backpack.
The winter bike has a full rear pannier rack with which I can use saddle bags for commuting and touring. Front rack, barbag and maybe even a triangle bag to follow.
I also have a large Ortlieb saddlebag and a frame bag I use on the 'good' bike for very light touring.
I'd try and avoid using more than a small-medium saddle bag and your back pockets if you're out on a leisure or training ride; if doing muddy MTB then small high quality backpack is a popular choice.