Lightweight inner tubes £15-20, makes a difference, lightweight skewers £15-20, don't make much difference but, like I said, this is an exercise in because you can :P That will probably save about 150-200g. Not sure what saddle is on there? But a stock saddle is usually a good place to save 100g or more. Can get a very light all carbon saddle on
eBay for £30-40 or so, I wouldn't readily trust it for every day use and abuse, but for Hill Climbs or just for the sake of saying you can, why not.
Could also hacksaw off any excess seatpost, just make sure to maintain enough to meet the minimum insertion amount, i.e. if the min insertion is marked as 6cm make sure at least that much of the post will still be in the frame once you chop it. On many seatposts this is encouraged by the manufacturer and doesn't void the warranty.
None of this stuff, bar maybe the inner tubes will have a perceptible performance benefit except on the steepest of balls out hill climbs, it is just fun
