Guild Wars 2: Heart of Thorns sees players having to obtain large amounts of experience points to earn Masteries. Masteries allow you to obtain new skills and abilities which help you in the jungle as well as core Tyria. With that in mind, it's really important to maximise your experience gain as it significantly reduces the time it takes to unlock them. Without boosters, simply completing events can take a fair amount of time. With boosters, that time can be cut down quite significantly and I'd recommend everyone use them as much as humanly possible. Before I get onto the list of Boosters you should be seeking out, I'll just mention some important things:

1. One of the best Boosters is only available on the Gem Store.

2. You can only stack one of the same type of Booster, using a similar type will replace the first.

3. To maximise experience gain you need to use independant experience Boosters (this can include items or food). 

Below is the list of Boosters you can gain, as an absolute maximum. Each Booster also directly links to the Guild Wars 2 Wiki so that you can read more on it. 

Improved Experience Booster: Provides +100% experience from kills - available from Black Lion Chests or the Gem Store

New Experience Booster: Provides +50% experience in All Game Types and up to 100% Bonus Experience for Kill Streaks - available from Black Lion Chests or the Gem Store

Birthday Booster: Provides +100% experience from kills - available from your yearly birthday

Guild Hero Banner: Provides +10% experience from kills - available from guilds who lay them down or your own guild if they can access it

Experienced Infusion: Provides +20% experience from kills - available from Hall of Memories or Laurel Merchant

Halloween Food (any on the Trading Post): Provides +15% experience from kills - just open some Candy Corn from the Trading Post

Powerful Potion of Slaying Scarlet's Armies: Provides +15% experience from kills - available from the Trading Post

+5% Kill Exp for 24 Hours Guild Buff (+5% from kills) - available only through your guild and under the old system, requires influence

Total Experience Gains: 305% additional experience from kills. 

Have I missed a buff? Let me know and I'll add it to the list.