I would recommend putting basic skill cards into your deck based upon deficiencies you may have. When performing a skill check, try to have a +2 bonus to the skill check. With a +2 bonus, you will make the skill check successfully the majority of the time. Place basic skill cards into the deck to ensure that you make these checks. Maybe you are a little light on agility symbols and want to ensure that you can evade. In this case, add two copies of Manual Dexterity into the deck. Guts is another basic skill card that I recommend adding to decks for characters that have low willpower scores.

When the game first came out, I had a difficult time with the third scenario in the core set. When you start building your collection, you feel very appreciative when you start swapping out less effective cards from your deck. I love the game because it was so difficult in the core set. When I did finish the core game with our play group, we all felt a sense of accomplishment. Keep at it, the more you play, the better you will get at it. I still play the core set often when playtesting.

The core campaign is THE hardest campaign in the game. I've played every expansion and it is crazy how much of a difference there is

I think for newer players, especially with a small collection, emergency cache is a solid choice. When people gain more experience at deck building and have a larger collection, I agree that you may not need to use the card any more.