Stuff to carry........
Camelbak while on the MTB 'cause I can't take my hands off the bars long enough to get out a water bottle! Or I'd crash, most likely.
Water bottles (2) while on the road. I find that I sweat soooooo much under the camelbak that I prefer not to wear it if I don't need it.
In the under-the-seat pak : tube, tools, money, insurance card, CO2 cartridges and inflator, lip balm and sunscreen (sm. size), red blinkie light. If I need more stuff than that, I wear a fanny pak. Annoying at first but you get used to it and it's so convenient - when you stop, you have stuff with you. Money, phone, female stuff, deodorant, camera. I can actually fit a lot more if I need to. Depends on the ride. If it's a race, everything is stripped to bare minumum for the least weight. If it's a fun ride, like RAGBRAI, then I carry lots of stuff, whatever might come in handy for the day. Otherwise, somewhere in between, never more than I have to.
Time is a companion that goes with us on a journey. It reminds us to cherish each moment, because it will never come again. What we leave behind is not as important as how we have lived." Captain Jean Luc Picard