If you mean within walking distance, this might not be easy. The closest to pubs was Riverside Camping in the centre of Betws-y-Coed, but I was in the area about 3 wks ago when I saw a sign at the end of the road to the site, saying it was closed for renovation. There's another camp site on the western end of the village but I've never used it.
I very highly recommend Rynys Farm as a camp site, £5 per person per night, it's off the A5 near Conway Falls but this is about 2.5 miles south of Betws-y-Coed and there's nothing near the site. There are 3 pubs in the village - I thought the food portions at The Stables were a bit small, the Pont-y-pair looked a bit pricey and I haven't tried the 3rd one at the other end. I don't know whether any of them do Guinness, don't like it myself, but generally speaking the choice of beer in North Wales pubs is very limited.
There's a big Wetherspoons in Llandudno, might serve Guiness, and the food could be worse, but there are no camp sites close. I drive there from Conwy Touring Park, it is inexpensive, has lots of facilities, but they make everyone use numbered pitches which can get rather muddy. It is on the B5106 about 2.5 miles south of Conwy.
The other one I can think of is the Forest Enterprise site off the main road 1.5 miles north of Beddgelert. The site has good facilities, but is a bit pricey and can get crowded. The village has 3 pubs which do meals. Once again, I don't know about Guinness.
Check out the sites at
www.ukcampsite.co.uk which has user reviews.