Can’t open upgrades menu in MvM

This is what people expect you to use, especially when you Mann Up:

• Scout
  • Mad milk: when upgraded, slows enemy by 35%
  • Fan O' War/Sandman: the enemy you last hit with this weapon will take minicrits (increased damage) for a while. (Note: the Sandman must be upgraded using 500 points to gain the minicrit effect, but is then much more useful as you can hit enemies with baseballs from far away.)
• Soldier
  • Buff banner: when you deal damage a bar fills on your screen. When the bar is red switch to the banner (press 2) and click. You and players near you will deal minicrits. When your rocket launcher is fully upgraded, you can get the buff banner going in as little as three rockets. You should be using your banner as often as possible.
• Engineer
  • Wrangler: use to boost your buildings' health and fire rate at the cost of automatic aiming plus a three second sentry deactivation time when you switch to other guns.
• Sniper
  • Jarate: throw at enemies. Soaked enemies take minicrits and, with an upgrade, are also slowed down.
• Medic
  • Kritzkrieg: the ubercharge makes your patient deal critical hits (×3 bonus damage)
• Spy
  • Dead ringer: the instant-on cloak and the 90% damage reduction that comes with it makes you a tough nut to crack without having to spend thousands on credits on resistances.
• All classes
  • Canteen: lets you spend money for four-second buffs. Guaranteed critical hits are the most expensive and popular canteens, but instant ammo refills are also very good (and a fraction of the cost). Engineers always want to have at least one instantaneous building upgrade canteen.

You can obtain the canteen by completing any Mann vs Machine mission. You can get everything else from any scrap banker such as scrap.tf.

People may also expect you to use the following, although you probably won't get berated as much if you don't:

• Demoman
  • Scottish resistance: sticky jumping is harder but you can lay down more stickies at a time, useful when combined with kritz ubers at setup time to lay down a nasty initial surprise for bots and tank.

The Strange wrench tracks both Kills with wrench and Sentry Kills. But, the item itself is only effected by Kills with the weapon, and the Sentry Kills are just tracked underneath it, much like Stange mediguns (not Kritzkreig) with their UberCharge being the main counter, and assists being the secondary counter.

Moving on, you would need the strange part: Robots Killed on a weapon, but it tracks kills with the weapon, not something it creates (like a sentry gun), as it would track only Melee kills. And, seeing that the PDA can not get any strange parts on it, there is no way to track sentry kills on MVM robots.

NOTE: If you are you using the Strange Gunslinger, it counts Sentry Kills as its main, then Melee Kills as its secondary.