With Version v61, tomes have finally been replaced with the Environment Magic spell "Enchant Item Collection" which is cast on a cut gem. However, I believe the information here still does a good job of explaining the uses for the spell, even if the details about obtaining them and charging them has changed.
Tome of Collection Edit
Tomes of Collection will pick up a specific item from a monster drop to your inventory for one charge. They are both a blessing, and one of the biggest money sinks currently in the game. To understand why we can examine the first sentence in this article a little closer: A specific Item - Each tome will only pick up one specific item, and rolls from a table of the over 350 items (and rising) currently in game to determine what will be picked up. From a monster drop - The tome does not collect an item generated from any other method than monster drops. Currently less than 1/5th of the items a tome can be rolled are dropped by a monster. To your inventory: The item picked up will not be noted, therefore generally only a tome for a stackable item is very useful, except in some edge cases. For one charge: Tomes charges are calculated by rolling a charge number of between 80,000 and 130,000 and dividing it by the value of the item. Therefore a high value item's tome may only have a handful of charges!
However, this information means we can easily work out the criteria for whether or not a tome is useful: High charges, the item droppped by a monster currently in game, preferably a monster than can be easily killed en-masse, and that item is stackable
Rerolling Tomes Edit
The Mysterious Man in Hyrill will reroll a tome to a new item for 1,000 coins each time. The charges of the tome will remain the same, but the targetted item will change. This is a good way of getting useful tomes while guaranteeing a high charge number. However, it is also extremely expensive! As stated above, each tome rolls on a table of over 350 items, therefore if you are hunting for a tome for a specific item you have a 1:350 chance (or around 0.3%) for each reroll, and many players have spent a million or more coins searching for a specific tome.
Because of this it is recommended to only reroll high charge tomes (80k charges or more) and to have multiple such tomes to roll, in case you get other high value targets.
Valuable Tomes Edit
|Tome of Collection||The so-called Tome of Tomes. Useful at Hobgoblins or Guards, to harvest multiple tomes.|
|Feathers||Gather feathers without having to pick them up! Was the gold standard of tomes before pick pocketting guards was added as a source of feathers.|
|Copper Arrows||Hobgoblin archers commonly drop a stack of copper arrows. This is an extremely efficient way of gaining arrows for range training.|
|Rock Spike||Rock Shell crabs have a 100% drop of these spikes, which are used to create ammo for the Anchor Crossbow - considered the best ranged training weapon in the game.|
|Shell Chest Key||Rock Shell Crabs also drop this key at a low rate. The key stacks, and the chest is one of the best sources of high tier cloth in the game. Expect approximately 8 keys per day using this tome.|
|Fiewon Teleport||Goblins commonly drop Fiewon teleports, which can be incinerated for 50 void shards, or used as is for Environment Magic experience|
|Coins||Less useful, as each single coin is a charge, so a 100k charge tome will provide 100k coins.|
|Void Essence||Hobgoblins have a rare drop of a single Void Essence. This is a slower source of void essence than Fiewon Teleport, but still useful|
|Iron Arrows||A less common drop than the copper arrows. Still quite useful as a supplement for ammunition when training on Hobgoblin Archers|
|Wolf Claws||Wolf Claws are dropped by all wolves, and are used to create Wolf Claw Arrows. The only reason this item isn't considered a more useful tome is that it is not currently possible to AFK Wolves for long periods, even with max melee, and full osmium armor.|
|Magic Scrolls||Can be useful when farming for these items, particularly the teleport varieties from guards. Currently there is no known areas to AFK farm drops of the wound scrolls, but still handy|
|Cloth||Because cloth does not stack, it is debatable whether or not having a cloth tome is useful, however in combination with bags provides a slight quality of life boost when farming cloth.|
Other Tomes to consider Edit
Hobgoblin archers also drop a noted oak bow. Golem Fragments and Chunks may be useful if you are planning on farming for a golem necklace, as occasionally you will miss the appearance of a golem. Red Wizards drop a number of items that could be useful to have a tome for, including high tier essences and cloth, however these are definitely not AFK-able. One could also speculatively collect tomes for items they think will see a boost in future updates.