I flew recently to SE Asia with Air France on the way out and KLM on the way back. Paid for an exit seat both ways, and thought it absolutely worthwhile for the extra legroom and direct aisle access, even if the KLM standard fee for this is a bit pricey. For fun, I also tried the 'A la carte' menu option (I went for 'Menu Tradition') on the AF flight, and thought that was worth the price too. It was served on a regular Economy meal tray, but the food was a bit different and tastier than a standard meal. Such options are available on AF flights out of Paris (though not on flights returning to Paris, I think). On the way back, just had a regular KLM Economy meal, but again was pleasantly surprised with the quality.
Yeah, my top budget travel tip at the moment is to pay ~£20 for an exit row seat on Norwegian - the extra space makes a massive difference and for £20 even on 13 hour flights to Singapore it's an absolute bargain!
My (not quite so budget) tip on Easyjet is to buy a half bottle of champagne for £16 - not really much more expensive than buying a couple of other drinks. Also, bring a nice picnic when flying LCCs.
