You can experiment right from the start in Dead Rising 2 by combining items together to create combo weapons. However, for the best weapons you will need to have the combo cards.
Most of these are gained via leveling up while some of these you get when you save particular survivor or you find them hidden throughout. You can read our full Dead Rising 2 Combo Cards Weapon Guide that covers the game and for the Case West DLC, you can refer to this guide.
Dead Rising 2: Case West Combo Card Weapon Guide
Defibrillators + Medical Tray
Zap N’ Shine
Floor Buffer + Electric Prod
Blast Frequency Gun + Electric Prod
Sickle + Katana Sword Location. In the living quarters there is a maintenance room with both the sickle and the katana.
Impact Hammer + Blast Frequency Gun Location. Impact Hammer is the weapon of Hamzat guys, keep playing till you come across them.