The /reclaim command in LOTRO is a way to get promotional items back that you may have deleted. The items you receive depends on what you are eligible for. E.g. if you have bought the LOTRO Mithril Edition, you are eligible for the reclaim on that. Note that not all promotional items are included in reclaims - most notably the ones that give XP tomes and similar.
You can use the command every 7 days on any character. Make sure to have enough slots in your inventory to have room for all of them. They are granted instantly when you type /reclaim.
Here is a list of known reclaim items that you might be eligible for. Please note that the list show the actual items you receive with the command. Items inside bundles are not shown here.