I wouldn't necessarily be raining. It hasn't rained where i live for a week. It might be cold out, but it is very traditional to have a bonfire and to roast food on that. Like potatoes, and other BBQ food, like Apollo13 said. It's cold this time of year, yes, but that's why we have the bonfire's and use them as the BBQ.
It's not the kind of holiday you would come home for. Not like Christmas. It's the kind of holiday you would go and see fireworks shows at, but you wouldn't make a special visit home for it.:)
But if it's a dry day/night then yes, a BBQ.
The Weasley's might have fun setting off fireworks (oh, the fun of writing Arthur in that story). The boys at home could make the bonfire and then they could all roast their food on it. Hope i helped. Have fun:)