I havent seen many people on here who consider themselves gloomcore but just in case!
Casual:
Overall shorts + oversized shirt under + combat/hiking boots
Black tank top + baggy jeans/cargo jeans + tennis shoes
Black shorts + tucked in shirt + combat/hiking boots
Black shorts + sweater vest
Swimming/beach trip:
One of those beach robes + dark colored swimsuit + sunglasses
Girly-ish:
Dark colored overall dress + white/grey shirt + combat/hiking boots
Black tennis skirt + light sweater (not for super hot days)
Lmk if you want more summer outfits for different aesthetics!