Here is my recommendation of accessories to have with you at all time during your rides.
#1 25mm fat tires
More comfortable and durable, 25mm and even 27mm if your frame can welcome them are a no-brainer for any cyclist.
#2 A frame fit long pump
Forget the Co2 cartridges and mini pump. Get the real deal and grab a frame-fit pump. You will achieve higher pressure with more ease and don't have to carry anything in your jersey pockets.
#3 A seat bag with the following
- a long valve replacement tube
- a super patch kit
- a 20$ bill
#4 A multi tool
Normally, you don't need it often, but when you do, you'll be grateful.
#4 A phone
The good old phone allows you to use the calling option and get help from a friend !