To improve the squad next season.
In order of priority for me:
Must haves:
1) Monster holding/defensive Midfielder: This will be controversial I know as our CF inadequacies have been well documented, but remember we did quite well for most of the season with Giroud up there despite all the grief he causes us. Going forward, this team is set up to maximize the qualities of the midfielders. Arteta is done unfortunately. We need a solid central midfielder to strengthen our core which is still shaky. Provide sound footing to launch our (counter) attacks, take some of the weight of defensive duty off our flair players. We won't be broken down or caught out as easily as we tend to do in the big games. Put an end to the American football score lines.
2) Top CF.
3) Right Fullback if Sagna leaves. While he is solid and consistent, I don't think Sagna is as irreplaceable as some do. There are a few good, maybe even better alternatives for our style of play out there.
Sort this out, keep the rest of team as is, and we're good for a sustainable challenge next year.