Probably wish he'd shut up and/or hole up somewhere I wouldn't have to see or hear him.

WWYDI you saw LotGK turn into her snaky self?

First I'd probably scream, then I'd feel for my sword. 😛

WWYDI you were able to join in the Snow Dance?

Probably get pegged at the very start. 😛

WWYDI you recognized the kingdom of the Sea People for what it was (ie: not just random shapes and schools of fish)?

Wonder in amazement and maybe fall overboard if I was leaning too far over. 😛

WWYDI Reepicheep fell overboard?

Desperately try to get someone to help him, I can't swim very well.

WWYDI you found out one of your animals knew the ways of the sword?

😯 Make me your padawan!!
😛

WWYDI went to Cair Paravel with a message from the king and found that the city had been taken by enemy forces?

I think I would run away and hope no one saw me.
WWYDI Reepicheep was leaving to go to the end of the world alone and you were Lucy?

Cry and try to make him stay, but eventually let him go.

WWYDI you were in the wood between worlds and forgot to mark which pool you came out of?

I would jump into a pool and hope it was the right one.

WWYDI you realized Aslan was telling you you couldn't come back to Narnia?

Cry, ask Him for last words of advice, promise to find Him in the other world, and finally cry some more and give Him a long, long, tight hug.

WWYDI a talking horse said that you could ride on him?

Ride, of course. And ask for pointers.
WWYDI the "wet blanket" member of your group turned out to be the best member of the group?

I would apologize for calling him that. 😀

WWYDI Narnians turned on the pevensies?

Plead with them to reconsider and then go join the Pevensies (unless the Narnians had turned on them for good reasons.)

WWYDI Narnia was taken over by talking slugs?

Threaten those slugs with a visit from Mandrake. 😛
Regardless of whether or not I do exactly that, I'd conspire to take Narnia back.

WWYDI you found Susan's horn?

I wouldn't want to touch it for some reason. 😀

WWYDI the telmarines captured Peter?