A few general things to consider and/or bring when you come on a foray are: 

1. Basket (plastic bags cause fungi to sweat and deteriorate quickly)
2. Paper bags (not plastic) to wrap fungi
3. Stout walking boots (not trainers) or wellingtons
4. Avoid wearing shorts (see Lyme Disease)
5. Sharp Knife 
6. A good field guide
7. Hand Magnifying Glass (for better identification in the field)
8. Notebook and pencil
9. Food and drink (lightweight packaging)
10. Basic first aid kit
11. Watch, mobile phone, map and compass
12. Always be aware of your surroundings, it is surprisingly easy to get lost even in a wood/forest that you think you are familiar with!
13. A pack of hand wet wipes or anti-bacterial hand gel
14. Insect Repellent (Mosquitoes in summer and autumn!)
15. Waterproof clothing if forecast is rain (The DFG do not often cancel unless conditions or the forecast are VERY inclement or become a risk to health & safety)