If teams are not willing to give a first round pick, and the Raiders have to give a pick and a player, I believe the most likely would be Bryan Edwards. The Raiders will not trade Ruggs, they just brought in John Brown, and players like Willie Snead and Zay Jones will not hold enough value to add to the trade.
I believe Edwards has a lot of potential and will be a good player for the Raiders, but if he is a piece that has to get shipped off for Adams, it is a no-brainer. In this scenario, Adams would join John Brown and Henry Ruggs out wide, being surrounded by a ton of speed and opening up the field a ton for guys like Waller and Renfrow.
Julio Jones was traded for a second and a fourth, but his age, injury history, and contract are what led to that. If Adams does somehow go for a second, then a solid, young piece at the position will likely be required, as well as a few other draft picks for the services of such an elite weapon.