The Class Trip event wraps up this Wednesday at 1pm EST, and you likely have left over S.H.I.E.L.D. Markers. After the event concludes, you will have an additional 7 days to spend any markers in the “Souvenir” section of the store.
If you are actively participating in alliance war, you will likely want to prioritize the Lesser Attack and Lesser Champion boosts, as spending markers on these now will save you units later.
After capping out on boosts, there are a number of catalysts available, with full T1a, and 7,200 T4b shards being the most relevant to end game players.
One nice bonus in the Souvenir store is that the cost per item does not increase with each additional purchase, like we sometimes see with featured items.
Whatever you decide to purchase, make sure you spend your excess markers before they expire on August 14.