If your celebration does not include the part in which you have to pour the blood into your own mouth, you can use red water paint. If you think that the conventional watercolor paint is too thin, use the fabric paint (it is sold at art stores) to cover your clothes in red. You can also use enamel or emulsion, but their stains are not that easily removable (you will need a thinner for that which can affect the fabric).
Artificial blood, which can be taken into mouth, should be made only from food components. For example, you can use the beet juice. To prepare artificial blood, boil beetroot in water, add starch in the resulting liquid until it thickens.
Another thing which can be helpful in this regard is thick strawberry syrup. You can buy it from the confectionery department of any supermarket. If necessary, add a little cornstarch to it. If you cannot buy strawberry syrup, you can take liquid chocolate and mix it with dry red food colour.
Ketchup can be another alternative to edible artificial blood. It is an item generally available off the shelf.