<confucius>The lightest, most compact kit is that which you leave behind</confucius>
Like most people you probably took too much on your first trip, a case of "just in case"

Make a list of everything you took, now cross off everything that you used, also cross off toolkit and first aid kit as these need to be on every trip. Look at what's left and ask yourself: "why did I take it?", Could you do without it for your next trip? Sometimes you don't use one piece of gear because another was used, for example, you took a warm cycling top and a waterproof, it rained so you used the waterproof but not the top.
There's no one correct list and you are unlikely to get it right every time, it's a continual learning process, it's also a multi-way balancing act between carrying too much kit, being comfortable, not carrying the right kit. Stu has a posting or two on this on the blog that are worth reading.
If you are just testing the waters to see if you like bikepacking then there's no point in buying loads of kit, you adapt what you have. Once you've got past that point it's a matter of where your priorities lie. Replace/update as and when you identify a problem with what you have, your setup needs to suit
you., if you need a 3 season sleeping bag in summer then that's what you need.