Go to Big Picture mode. Find LoTRO and use 'Show serial'. Copy the code and paste it to myaccount.turbine.com.
Ideal for activating of F2P account that has no other content.
What does this give you?
First of all, 500 Turbine Points that you can use for purchasing other content. Quest packs are mostly more expensive than 500 TPs, but as a rule you shall never buy anything on normal price in the LoTRO store. Wait for sales/coupons.
Second, Evendim quest pack. Should cover levels from 25 up to 41 (I mean for quests and slayer deeds - can't go further as mobs will have way lower level than player's toon). But Evendim means access to Annuminas instances, and they're scalable from 40 to level cap. Three instances in total, so that's not bad.
Steely Dawn cosmetics - not many people use this but you may meet someone using this. It's not very special cosmetics set but at least it is a set. Too bad it can't by dyed.
XP boosts - nice but bound to character only.
Don't buy this unless it's dirt cheap or free. And I know a website where you can get it without paying a nickle.
Don't buy it on normal price, but if you can snatch it from elsewhere it's gonna boost your account.