Trick-or-Treat Bags(ToTs) are festival item containers from the annual Halloween event. Each time you open one, you will receive multiple items from a list you can find here. ToTs currently sell for around 4s77c per bag on the trading post, with buy orders sitting at around 4 silver. ToTs present an interesting gamble, because unlike most of the similar gambles GW2 has to offer, ToTs can open to reveal several items of value which will net you large profits, including a killer jackpot. Unfortunately, for everything good that can come out of a bag there is about 5 things you don't want, so if you don't want to be spending time cleaning your inventory after opening a bunch of bags then this one probably isn't for you. So what can I get you may ask? For a start they can drop 7 unique exotic weapons, which value between 2 to 8 gold each on the trading post, and a Karka helmet skin worth about 12 gold too! A few miniatures can also drop, with one in particular being worth about 17 gold - not bad for some of the more uncommon drops! Next up some of the rarer drops, including 3 gifts: Souls, Spiders and the Moon, worth about 20, 3 and 9 gold each respectively. Then we have some more rare drops in the form of some cosmetically-enchancing necklaces! The Oontz's Necklaces drop as account-bound gear but can be salvaged to obtain the unique Poly-luminescent Undulating Refractors. There are 4 different types: black, green, orange and teal, and they are worth 64, 18, 23 and 30 gold each respectively. Nearing the end now, we have the very rare Unopened Bottle of Batwing Brew which is required to craft the Nightfury shoulder skin. If you're lucky enough to land this little gem, you'll be rewarded with about 85 gold! Lastly we have the uber-rare jackpot find; the Phospholuminescent Infusion, which again is a cosmetically-enhancing upgrade component. However, unlike the Refractors, this is an ascended infusion which can be slotted into ascended gear, making it more desirable. This item has an extremely low drop rate and if you somehow manage to bag one you'll be looking at a 1200+ gold payday!
Wintersday Gifts are the Wintersday(Christmas) festival equivelent of ToTs. You can find the contents of these gifts here. These containers are arguably the inferior gamble, and while the price per gift is roughly the same as ToTs which may lead you to believe otherwise, this is largely driven by the alcoholic beverage drops which you need to consume(10,000 of them!) to complete an achievement in order to obtain the Winter's Presence shoulder skin. With that said, it is still worth noting that Wintersday Gifts still contain some valuable items, once again including a jackpot prize. There are a few miniatures, namely the Festive Golem, Snowman and Tiny Snowball worth around 9, 12 and 2.5 gold each respectively. There is also an Enchanted Snowball Box which opens to reveal an account-bound endless snowball tonic - the initial box can be sold however, for about 12 gold! Next up there are 2 very(equally?) rare recipes for some unique ascended backpieces. The reason why I question whether they are equally rare drops however is because of their incredible difference in trading post value. The Shadow of Grenth recipe can be sold for about 6.5 gold. The Light of Dwayna recipe however will net you an incredible 120 gold! It is unknown whether the difference in price is a result of differing drop rates, or if it is simply down to a heavy difference in demand for each item. Lastly the jackpot item, which is again the Wintersday equivelent of the ToTs jackpot, the Winter's Heart Infusion is another cosmetically-enhancing upgrade component which will grant you a wopping 850 gold when sold on the trading post!
I couldn't write a post about gambling in Guild Wars 2 without mentioning the ectoplasm gamble. There is an NPC in Lion's Arch called Apprentice Mekteki. This NPC sells ectoplasm containers called Destabilized Ectoplasm. They come in 3 different sizes from small to large: Dab, Clump and Glob. Effectively what is happening, is you are paying a combination of gold and Globs of Ectoplasm to receive a container which will yield varying amounts of.. gold and Globs of Ectoplasm. What? Yes you did read that correctly. The contents include varying different trophies named Crystallized Plasma which can be sold to vendors for liquid gold. They also contain varying amounts of Globs of Ectoplasm. It should be noted that this gamble has been proven to yield lower returns than inputs over a prolonged amount of attempts - this should be an obvious fact across the large majority of gambles. However that doesn't mean it can't make you rich. The Glob of Destabilized Ectoplasm is the most expensive container, costing 250 Globs of Ectoplasm and 100 gold. The jackpot from this container? 2500 Globs of Ectoplasm and 2000 gold. Not bad. Not bad at all.
Obviously there are plenty of other ways to gamble in Guild Wars 2, so here are a few honorable mentions: Crafting Mystic Clovers for profit, throwing rare or exotic weapons in the Mystic Forge for precursors, Mystic Forge material promotion and even opening other containers. So whether you are a gambling person or not, this is some useful information of how to acquire certain items. Gamble sensibly and enjoy!