It varies quite significantly from lounge to lounge, and as others have advised, do check which amenities are offered before you visit a lounge to avoid disappointment. Many do offer an open bar, some offer a single drink voucher upon entry with further alcoholic drinks available for purchase, and others require you to purchase all alcohol. I used my PP card extensively over 10 weeks of travel to Asia, Europe and North America (only reached QF WP/OWE this month so before then I had no status lounge access besides VA SG), so I feel I can say that the lounges in the USA seem to be of a slightly lower standard than one experiences in Asia and Europe. If it helps, here are my opinions of the lounges that I've visited on the Priority Pass card:
HKG East: Perhaps the NICEST PP lounge I've been in... brilliant atmosphere, powerpoints were plentiful, a large number of hot food options (all 'free'), and a good selection of soft drinks. Alcohol a/v for purchase.
Venice Marco Polo Club: Great views of the runway (and has a deck for better views/photo taking). Free wi-fi (you have to show your passport and get a card), decent coffee, comfy lounges, and powerpoints were available rather easily. Morning departure, so I'm not sure about alcohol (just check the site)
Vienna: Respectable food selection including some scrumptious dessert choices, self-serve alcohol (inc. premium spirits). The lounge also has an Amex VIP room - if you show your Platinum/Diamond/Centurion card to the reception they will let you use it... it was a nice quiet place to watch the tennis (and you can bring your food/drink in from the main room). Sliding glass doors keep the room private.
Frankfurt (terminal QF uses): Very nice atmosphere with a view of the landside roads. Self-serve alcohol including *some* premium spirits (Baileys and a few others). Food limited to snack items and sandwich quarters. Lounge was positioned in a way that made it 'hidden' (if you didn't know that it was there, you wouldn't find it). You need to ring the doorbell to have the door unlocked.
Singapore Rainforest lounge: Alcohol only by purchase, though there were a large number of food and drink items available (almost an entire wing of the lounge is dedicated to food/bev). Showers were great, and feature the appropriate amenities if you forget to bring your own. Power points located at tables near the walls only.
Melbourne United Club: Not worth getting here early. Some self-serve alcohol available and a few limited food choices. Lounge had a very dated feel (... to match the aircraft I assume

)
LAX TBIT KAL/Skyteam lounge: Some self-serve spirits and wine, coffee, very fast wi-fi (until the lounge is near capacity, then it's nothing to write home about), some snack food choices. What really p**sed me off though was that the entire lounge has just ONE SHOWER!!!
Newark United club: free wi-fi, decent breakfast selections. The one we visited had a view of gate A17 (United 93 9/11).
Quebec Salon VIP Lounge: Great views of the tarmac, self-serve alcohol, and even has a fireplace!! Unable to locate powerpoints easily, though I didn't need them on this occasion.
Chicago ORD UA Club: Plenty of room and powerpoints were plentiful, free wi-fi but alcohol needed to be purchased. Probably the nicest United lounge I've been in.
Vancouver Plaza lounge (USA departures): Nice selection of hot and cold foods, alcohol available for purchase. My tip for this lounge: sit near the glass panes that face the international arrivals area. By sitting near one of the gaps in the glass, you can hear the waterfall and it's quite relaxing!
Vegas United Club: Free alcohol including *some* premium spirits. Other premium selections a/v for purchase. Friendly staff and good views of the tarmac and of the Vegas skyline.
LAX TBIT Relax Lounge: Voucher given upon entry for one glass of wine. Further drinks for purchase. Lounge does not have bathrooms (but are located just outside). Wi-fi worked well and the staff were pleasant. We were able to buy hot food from the food court and bring it into the lounge without issue.
Hope that helps! Any questions, feel free to ask
