Which item(s) should I spend points on in warmane store?

Points suggestions only please for I am poor now.

80 arcane mage undead
2.7k Gearscore
32000 Honor points
3k Gold

Thanks

I have 18.4 points

I'd say Flare of Heavens (trinket), it's rlly good trinket with high SP proc.

my advice is pve mainly, but might apply to pvp: trinkets are most important for dps, then relic slot (wand) and weapons. After this, chest, head, legs; then hands feet, and then the rest.
make sure you have the icecrown rep farm ring, cause that's bis for pvp and pve.

I know where and how to get the rep, but where do I get the ring from?

I was looking at that as well. For anyone who disagrees speak now or forever hold your peace...

At 2700 gs, you're close to enabling RDF HC (to start the EoF collection and significantly boost EOT collection beyond 2 per day from RDF).

FOS/POS normal and HC have enough drop to gear a mage except for the following:
No head (wait for 75 EOT head)
Only 1 ring (wait for 35 EOT ring)
Only 1 trinket (wait for 50 EOT trinket)

So maybe consider using points to get those 3 things if you can't wait for the EOT to add up. Just one item (replacing your weakest, may quickly enable RDF HC).

Staff from point shop is also good option. Better than i219 FOS/POS drop.

For the ICC rep ring, after you reached Friendly, simply go visit the ICC quartermaster (inside ICC) to get it. If you're not in a raid, simply ask to group with someone and convert your party to raid, fly there, get ring.