Day 2 of the update introduces us to the new weapon upgrades and the so called "Canteens". Moreover, Valve presents a second MVM-Map: Coal Town.

The Upgrades

As mentioned in the news for day 1 of the Mann vs. Machine Update, robots loose credits when they are destroyed. You should pick up these credits, since they grant you the possibilty of buying upgrades for your weapons between the rounds for enhanicng your fight against the upcoming stronger waves.

However, there are no such upgrades as "Red-Dot-Sight" or "Grip", made famous by games like Call Of Duty, but you can improve your weapon's level, similar to Role Playing Games. You can buy "points" for different attributes, such as "more damage" and "firing speed". If all "points" for one attribute are bought, it is not further upgradable, since every attribute has a limited number of buyable "points" The picture below explains the system in a rather precise way. Apropos: you get to the picture by clicking on the  Grenade Launcher on the official Team Fortress 2 Mann vs. Machine web page.

The Canteens & the new map Coal Town

The Canteens provide the carrier with special abilites, for example 100% critical hits. Canteens occupy the Action Slot and you get them after every accomplished Mann vs. Machine mission. Every Canteen can be used three times. You activate the effect by simply pressing the Action button.

It remains unclear, wether the Canteens will be available for game modes beyond the Mann vs. Machine game modes, or wether they are tradable. I personally doubt this.

The picture shows five different Canteens but there is probably a sixth one, since one photo is ripped off( low right hand corner). All available canteens and their respective effects are listed in the TF2 Wiki. 

Furthermore, Valve presentend a new map for the Mann vs. Machine game mode: Coal Town.