Find an old pair of natural color or sheer white/gray pantyhose and trim the “feet” off. Carefully fill the hose with cotton or cut up cloth (old bed sheets work well for this). If you want to give a really nasty view, add shells or other “sharp” looking objects. Using a hot glue gun seal the ends. Draw “Veins” with a red marker
Randomly twist your intestines and stitch them in various places to make them appear more realistic. Spray them thoroughly with clear varnish & let them dry. This will give them a nice glossy sheen.
Place some Fake Blood in a small spritz bottle, and spritz in several areas to give them that freshly gutted look. Hang them from a torn shirt, or let them hang out over the top of your pants as though you had surgery that the doctor didn’t bother to complete!
Here’s an example, however, they opted not to draw on the veins, which does take a bit of time. If you’re going to make them, draw the veins BEFORE you douse them in fake blood or the marker will bleed and look terrible.