Where can my supporters hand me drinks or food during a race?

The organiser (or technical delegate) decides how much personal seconding is allowed and must state it in the race rules. Unless the race rules prohibit or restrict it, ASA Rule 33.8 says:

• Seconds may help you only at designated refreshment stations, inside the area the organiser marks out.
• If the area isn't marked, help must happen within 100m either side of the first or last table.
• Seconds may not enter the course, obstruct runners, or run beside you while you take a drink.
• No seconding from any vehicle, including bicycles and motorbikes, moving or stationary.
• If the organiser restricts personal seconding, it must provide refreshment stations at least every 3km, unless the province approves otherwise and it is clearly stated in the race information.

In ultra-marathons you're entitled to support from a handler (friends, family, coaches), subject to any restrictions the organiser sets.