There are a couple of eating options before you go through Security: a café, a donut stand and a sandwich stall. After Passport Control, Terminal 5 has over 30 food and drink venues to choose from, including a steakhouse, an Asian kitchen, tapas, express ready-made food counters and family-friendly pizzerias. The sushi here has been widely praised.
If you've got some time before your flight, get a shoe shine or try out the BeRelax Spa.
The latter offers hairdressing, pedicures and manicures, table and chair massages, and oxygen and aromatherapy treatments. You'll find it at Gates 6-7.