Which sort of foods should i eat before a blood donation?

Nothing special: Just be well hydrated. There is no special diet required.

~1hr before...: ...A light snack and prehydrate with about 1/2-1 liter of your preferred beverage. Shouldn't donate w/full stomach w/heavy meal, as may get nausea just as likely as if on empty stomach. Few days before, iron-rich foods (red meat if so inclined), dark greens, good nutritious food so body has what it will need to start to replace lost unit. Continue after for 1-2 days while replenishing loss.