As far as I know, there are no food which could help, even though people will always try to sell vitamins and foods telling they are doing wonders healing your body.

Light exercise, avoiding sitting and laying down is important. If you do anything more heavy like go to the gym, make sure you do everything the right way.

Light exercise will make you heal faster, even though sciatica is a real slow healer.

If you want to pick on some cheap foods which are good for you, buy some ginger root. Cut 5-10 small slices of it and peel them, put in ½ liters of water and cook it for 30 minutes. Then drink it. Best health drink you can find.