Your wallet can be exploited by moving to the top left and clicking on the Wallet button.
Treva is a currency that can be garnered by entering into PvP maps (the maps on the top-left of the map) and killing elite bosses. These elite monsters can be located by searching your minimap and should be pinpointed by a small red dot. If you don't see any, you can start slaughtering random monsters or shift channels. You can quickly switch channels with the /next-channel, /backchannel, or /move channel number_here commands (type /? to see the commands). Killing these elite monsters give you a chance at creating a portal to the Twisted Pocket Realm. These portals last for a few seconds, and once you go through, you will be teleported to one of the different Twisted Pocket Realm "minigames" (butchering a boss, butchering rainbow slimes, butchering chests, butchering mobs from an ambush, sabotaging towers). In the butchering of rainbow slimes and chests, you will be rewarded with Treva for each one you kill, and completing the other game modes will make for 4 chests to spawn at the end that spits up Treva and Mesos when opened. There is a probability that these chests turns out to be golden when they are opened, which will grant you more Treva than normal. You can consume Treva by visiting Queenstown and locating the shadow merchants at the top right. One of the vendors offers a glove that gives you 5.4% physical/magic piercing, which is a great placeholder until you get something better. You can also spend your Treva on Gem Dust boxes or Tier 1 gemstone boxes.
Personally, farming Treva with another player would be much more efficient than solo action. Although you have no choice but splitting your rewards in a co-operation, it is much faster since the elite monsters will sometimes have shields that switch between physical resistant to magic resistant.
Rue is garnered through the “Hoard Things” daily missions (each mission gives 4 Rues) or by completing the World Boss Daily Missions offered by the NPC (Aliyar) in Queenstown (each World Boss Daily Mission gives 1 Rue and 5 Blue/Red stars). Rue can be consumed by visiting the vendor in Queenstown. The most outstanding items that you can purchase from this vendor is the 60-Metacell Jar for 4 Rue, and the incredibly powerful Spicy Maple Noodles for 40 Rue, which is a consumable that implant an item on the floor that multiple players in your party can pick up, granting them 6% extra damage for 15 minutes. This is pretty helpful for Chaos Raids.
Havi Fruit is obtained through Dark Descent and can be consumed by visiting the Havi Fruit vendor in Queenstown. Probably the best thing from the vendor is the Swallowed Darkness gloves for 800 Havi Fruit, which gives some pretty great stats. It lasts for only 3 days though and cannot be enchanted. Supposedly there is a weekly quest that you can accept at the Stonehill Dig Site that rewards you with extra Havi Fruit, but it seems to have been removed or not implemented yet.
You can consume these red stars at red star vendors (such as in Queenstown). You can harvest Red Stars from completing the daily World Boss Missions in Queenstown (gives 5 red/blue stars) or by questing the hard dungeons. This vendor has many good tonics and lapentiers, including the extremely powerful Rooted Strength Lapentier. The vendor also sells Metacells.
You can consume these blue stars at blue star vendors (such as in Queenstown). You can garner Blue Stars from completing the daily World Boss Missions in Queenstown (gives 5 red/blue stars) or by unlocking the chests you obtain when you complete 1/3/5/10/15/20/25/30 dungeons per week. You can also harvest them from doing the “Hoard Everything” daily. The most notable rewards from the vendors are the tonics, the Metacells, the Life Drain Lapentier, and the Shockwave Lapentier.