Based on the Marvel Previews #32, March for May 2015, I'd say you need to pre-order the following books in order to keep up with Spider-Man.
Core Titles
Amazing Spider-Man #18
Amazing Spider-Man #18, variant cover NYC
Amazing Spider-Man #18, variant cover Stacey Lee
Amazing Spider-Man #18.1, variant cover Greg Land
Amazing Spider-Man #18.1
Marvel Universe Ultimate Spider-Man: Web Warriors #7
Spider-Man 2099 #12
Spider-Verse #1
Spider-Verse #1, variant cover Robbi Rodriquez
Guest Apps
All-New Captain America Special #1
All-New Captain America Special #1, variant cover Adam Kubert
Captain America & The Mighty Avengers #8
Howard The Duck, variant cover Jason Latour #3
Old Man Logan #1
Old Man Logan #1, blank variant cover
Old Man Logan #1, variant cover Andrea Sorrentino
Old Man Logan #1, variant cover Skottie Young
Old Man Logan #1, variant cover Steve Mcniven
S.H.I.E.L.D. #6
S.H.I.E.L.D. #6, variant cover TBA
Secret Wars #1
Secret Wars #1, action figure variant John Tyler Christopher
Secret Wars #1, action figure variant John Tyler Christopher
Secret Wars #1, blank variant cover
Secret Wars #1, clasic variant cover Butch Guice
Secret Wars #1, connecting variant cover Simone Bianchi
Secret Wars #1, party variant cover Chip Zdarsky
Secret Wars #1, party Variant Sketch Cover Chip Zdarsky
Secret Wars #1, variant cover Amanda connor
Secret Wars #1, variant cover Esad Ribic
Secret Wars #1, variant cover Jim Cheung
Secret Wars #1, variant cover Skottie Young
Secret Wars #2
Secret Wars #2, clasic variant cover Kevin Nowlan
Secret Wars #2, connecting variant cover Simone Bianchi
Secret Wars #2, variant cover Esad Ribic
Secret Wars #2, variant cover Yasmine Putri
Secret Wars: Battleworld #1
Secret Wars: Battleworld #1, Action Figure variant cover John Tyler Christopher
Secret Wars: Battleworld #1, variant cover James Stokoe
Ultimate End #1
Ultimate End #1, variant cover David Marquez
Ultimate End #1, variant cover John Tyler Christopher
Ultimate End #1, variant cover Skottie Young
Spin-Offs
Silk #4
Spider-Gwen #4
Reprints
Ant-Man: Scott Lang TPB
Marvel Firsts: The 1990s Omnibus HC
Miles Morales: The Ultimate Spider-Man, Vol.2: Revelations TPB
Ultimate Marvel Omnibus Vol. 1 HC