All tokens you can hand in at NPC's that are through Middle-Earth during this 5th Anniversary. One of the most easyst one to find is the Bree Town one. The NPC is standing at the boar fountain (south of the Prancing Pony) where you also get the quest for the Envelope gathering.
The tokens you can trade in for gift boxes that gives some random on level items or for marks.
The answer given is fair enough. To expand on it slightly, what you want is ANY 'keeper of gifts' NPC, of which Emma Bywood is one. There are several scattered amongst the major population centers of middle earth, whilst the anniversary festival runs. Once the festival is over - current end date may 9th? then the only options you have left are either to wait for next years festival, or trade them in for marks - Tad Leafcutter, at the bree hunting lodge, will do that for you, if needed.
I have to agree with spending them for skirmish marks is the best way. The Calenard Tokens brought me a Worn Symbol of Celebrimbor and I head of a guy getting a Worn Symbol of the Elder King in a Westfold-Giftbox as well.
I've burnt quite a few on the random gifts. Nothing major. But it looks like most of the higher level weapons are bought with marks, so I am saving them to trade. A lot of what is bought with marks doesn't look interesting to me, not sure what the skirmishes are, not curious enough to find out. But weapons and recipes I'm always interested in.
Skirmishes are mini instances that can be done by one person or a group. If you're still low level don't worry about them, but do save some skirmish marks if you're following the epic story - in Moria and Mirkwood a few of the epic chapters are skirmishes, and having a levelled up soldier helps. And since it's raining down skirmish tokens at a far better rate than you'd earn them in skirmishes...
Plus there's all kinds of neat stuff for sale in skirmish camps, from class quest items, to rare crafting components, legendary items and the things you need to go with them, gear, sone fun cosmetics, a lot of your personal LoTRO economy runs on having enough marks to buy things in skirmish camps.