My friend wants something summery and light. We have gin, bourbon, elderflower syrup, ginger, beer, Triple Sec, St Germain’s, Angostura, and orange bitters.

If your friend is looking for a summery and light cocktail, the "Summer Gin Granita" might be an excellent choice, especially since it includes ingredients you already have on hand—gin, elderflower syrup (a good substitute for elderflower cordial), and it’s designed to be a refreshing sipper. Given its overall rating of 4.37/5, it's a crowd-pleaser and perfect for a hot day. The blend of lemon juice, gin, apple vodka, elderflower, and watermelon juice creates a deliciously fruity and cool treat, although note that it might require some prep work as it’s served chilled but not shaken or stirred.

Another fantastic option could be the "Sapphire Summer Cup." It's not only rated highly at 4.23/5 but also packed with fresh, vibrant ingredients like mint, ginger ale, strawberries, lemon, and cucumber. It’s stirred gently to maintain the integrity of the fruit and herbs, making it a light but flavorful choice. While it doesn’t strictly include elderflower syrup or St. Germain’s, you could likely add a splash for a floral twist to match your ingredients on hand and elevate the summery feel.

For a straightforward and refreshing take, consider mixing up an "Elderflower Gin & Tonic," even though it's rated slightly lower at 3.99/5. Adding elderflower liqueur to your classic gin and tonic enhances it with a delicate floral note, perfect for summer evenings. This cocktail is simple to prepare and emphasizes the botanicals of gin balanced out with crisp, tonic water and a zesty hint from a lime wedge.

These options will definitely capture the essence of summer and complement the ingredients you have, making sure your gathering is both refreshing and enjoyable.