Look for any used Hollowtech crankset. The more expensive, the lighter. You can find LX for about £50 and XT for a bit more.
Just type in light weight pedals and choose whichever take your fancy. Magnesium are lighter and titanium shafts lighter still but more expensive.
For the forks, you have to look up the specs to get the weight, and you have to decide if you want to save weight by going rigid. For Suspension ones, Rockshox Reba.
Your stem looks like a heavy one. You have to look at weights of potential replacements, whuch they normally include in the listing info.
There's loads of cheap CF bars from Chines supliers on Ebay. Take your pick.
Same with seats, you have to look at the listed weights. Again, ones with titanium rails are lighter but more expensive. You can also save a bit of weight on the seat pin if you have a crappy one.
You have to do Google research for your tyres. You need to consider puncture protection and rolling resistance in relation to weight. I guess you can't have all three, but should be able to get a good compromise. Going down on width saves a lot of weight. If you only ride on the road, you don't need fat knobbly MTB tyres.
When you've sorted the main components, look at everything. Get rid of all the accessories that you don't need.
Don't forget that it costs a lot less to save weight from yourself.
