Are there cards (shop deck) that are so good you do whatever it takes to purchase them? If so which and why?

What about class cards? Do you buy a one xp card or save for a two/three xp card? Why?

It really depends on the party, but if you've got a mage, "Rune Plate" is phenomenal armor, since it offers good protection, but does not prohibit the equipping of runes. Also, you can't really go wrong with "Mana Weave," though it's pricey. I've passed up almost every other item, depending on the circumstances.

While it may be somewhat costly at 125 gold, I don't think you can pass up on Mana Weave if it is available, especially early. The reason for this is simple. It is the only such card that exists in ACT I and ACT II, for all expansions to date.

Further, while it is a Rune, since all heroes can equip any kind of weapon (although they may not get the best use of it based on their skill cards), the ability to automatically add 1 Surge to any attack can be huge, and can be decisive.

Pair this with many weapons from ACT I and ACT II that have the ability to add damage and/or conditions, this could basically be an automatic success (assuming you don't roll an X). This is especially true for Blue-Red attacks where it is more difficult to generate surges.

Finally, even if you have no need for the surge on your attacks, getting a free surge for every attack that hits means that you can always recover at least 1 fatigue - and this can be very valuable when you have many skill cards that often require the expenditure of fatigue to make use of them.

Just my two cents worth, but if you can get Mana Weave early, it can be a game changer.

EDIT: One other ACT I weapon that can be very nice is the Crossbow (175 gold), as it has multiple abilities that make it very nice. First, it has a native Pierce 1 which can be handy in eliminating defensive shields that are rolled.

Further, a surge can add +2 damage.

But ***MOST*** important, is that for a surge, it can do 1 damage PLUS move the targeted monster (no matter the size) 1 space. This can be crucial if you have heroes with abilities/weapons that have no way to do this. It can prevent or reduce the OL ability of using monsters to block small corridors, etc.

Since it rolls Blue-Yellow, the chances of getting a surge are pretty good. In addition, you could always pair it with something like say, MANA WEAVE, and get an automatic surge.

For all of that goodness, the Crossbow is only a one handed weapon, so you could also equip some form of shield as well.

I don't like that one bit! The heroes in my LoR campaign had the luck to get this

A strange man offers you a gold key.

The heroes choose a scout and place this card in his play area. He may discard this card this card during the shopping phase to draw 3 additional Shop Item cards.

travel event and of course bought the Mana Weave that was among the items (after winning the 2nd quest) This does not bode well for poor OL me..

While the cards mentioned above are probably the overall best, I think the Bearded Axe and the Ring of Power are worth mentioning too. The bearded axe has automatic pierce 1 and can turn that into a total of pierce 3 with a surge. If your victim can't roll at least 4 shields (hard to do in act 1), the attack gets an additional 2 hearts and it rolls a blue and red. That's pretty good damage output for act 1.

The Ring of Power grants the wielder (is wielder a word?) 1 additional stamina which is useful for any hero in all kinds of situations.

Overall I'd say the Mana Weave is the best tho. Just from the sheer utility of it.

I had Leoric as a Runemaster, equipped with Mana Weave. Suffice to say, he pretty much took care of business.