I'm not Phil Giamon counting grams to tackle climbing KOMs on a sub-14 lb bike. He has an assistant following to record the rides, and carry his stuff.

I ride a 25 lb steel road bike. A few grams or ounces here and there won't matter.

Especially in summer when I'm carry two or three 24 oz water bottles, and possibly a collapsible Mylar water pouch in a jersey pocket. On some rural rides the next convenience store or other source of water may be 10 miles away. That's a long distance when the temp is over 100F and I'm out of water.

If I'm on my road bike, keys go in my jersey pocket. If I'm on my hybrid, I'm probably wearing baggy shorts or jeans -- keys go in a pants pocket.

I've made a few concessions, mostly to bulk rather than weight. Fewer keys. A mini-wallet with only my ID, VA card and debit card, and a $5 or larger bill tucked inside. A phone always goes with me, especially after being hit by a car last year. Ditto a video camera, since the driver lied about the traffic signal to cover for looking down at her phone instead of the road.

Other stuff goes into a Serfas Speed Bag. I've switched from regular patch kits with cement tubes to Lezyne self sticking patch kits -- half the size of a credit card and only slightly thicker. They work. Saves bulk and weight.

If I eat gels or energy bars during a ride, I tuck the wrappers inside my shorts leg or sock -- sometimes in the saddle bag if I've stopped to have a snack. I wouldn't trust that method to retain anything important like keys. Although the compression socks I sometimes wear would hold a wallet and keys securely, but the weight would be annoying.