Slayer is one of the slowest skills in the grindy Old School RuneScape. You can however become a little more efficient at it in a few ways. First, using fewer consumables along with killing certain good money-making slayer monsters will make you more efficient by giving you XP, besides OSRS gold.
Secondly, saving inventory space means less loot left on the ground and more loot taken back to the bank in fewer trips. Getting additional or faster experience is also handy as it translates to more XP per hour, taking you closer to the 99s, or your next level goal. In short, these items are a must-have because they will make your slayer life a bit or a lot easier.
The Expeditious Bracelet
This slayer must-have item is designed to speed up the tasks you dislike by giving you a 25 percent chance that a monster you kill counts as two, so you should use it on the tasks you hate the most. It has 30 charges and one will get consumed each time the bracelet activates, so you only need to wear it when the slayer monster dies. You can create the Expeditious Bracelet by using LVL-1 enchant on an opal bracelet or by buying it from the Grand Exchange.
The Soul Bearer
To get the Soul Bearer you have to complete the miniquest Bear Your Soul which you can start by reading the book called Soul Journey, found in the Arceuus Library. The Soul Bearer is extremely useful for tasks with monsters that drop ensouled heads, such as demons, trolls, elves, giants, dagannoths. It allows you to send the ensouled heads straight to your bank, thus helping you save inventory space useful for other loot. The Soul Bearer consumes a charge for each ensouled head sent to the bank and can be charged with one soul and one blood rune per charge.
The Herb Sack
The Herb Sack is exceptionally useful in saving inventory space. It is handy for a lot of tasks but extremely useful for monsters that drop a lot of herbs such as aberrant spectres, turoths, or kursaks. You can only get it by buying it for 750 slayer points or 250 Tithe Farm points at 58 Herblore. It stores up to 30 of each type of herb, in their grimmy form.
The Rune Pouch is one of the items you should use for every task. It won't only help you with your slayer tasks, but with many-many other activities in OSRS. You can buy it for 750 slayer points from slayer masters, for 75 Last Man Standing points from Justine’s shop, or you can buy its noted form from other players on the Grand Exchange. You can store up to 16k runes of three types in it.
Make sure to speak with the magic tutor in Lumbridge to toggle on that the runes you pick up from the ground go straight in the Rune Pouch. This can be extremely handy if you keep dust and fire runes in the pouch on a dust devil task and for other slayer monsters that drop runes that you want to pick up.
gem bag on skeletal wyvern background
You’ll find that the Gem Bag is suitable for most tasks since most slayer monsters have access to the rare drop table and will most likely drop gems. You can get it for 100 Golden nuggets obtained while mining in the Motherload Mine, and you can store up to 60 of the following five types of uncut gems in it, for a total of 300: sapphire, emerald, ruby, diamond, and dragonstone.
seed box on tithe farm background
The seed box is another must-have slayer item that will help you get the most out of your inventory by saving up to five spaces, since you can store six different seed types in it.
You can count on it whenever you are assigned a task with slayer monsters that drop loads of seeds like dagannoths, turoths, kursaks, moss giants, fire giants, or aberrant spectres. To obtain the seed box you'll need to slowly obtain Tithe Farm points from playing the minigame and buy it for 250 points.