Yes, and this is very important. Look in the mirror, and repeat the following mantra: EAT. CELEBRATE. BE HEALTHY.
Seriously, I know that some traditions require a 24-hour fast before ritual, but if you're not part of those traditions then that rule doesn't have to apply to you. More importantly, you need to take care of yourself and your health. If you're new to Pagan practice, and you're following a tradition that is more eclectic than established, then there's no reason you should make yourself ill by following a guideline from someone else's rulebook.
Now, does this mean no one should ever fast? Certainly not, but there's a time and a place for everything - and not all ritual preparation applies universally to everyone. If you're going to do a ritual fast, make sure you're medically able to do so. For more on ceremonial fasting, read Ritual Fasting. While some traditions require that you abstain from food, drink, alcohol or even sex for a certain period before ritual, not all require it. Again, it depends on your particular tradition. As someone who's still seeking and learning, you'll need to explore a lot of different flavors of Paganism before you find the path that's right for you. And if a book is telling you that you must fast before ritual, if you've got a medical condition you need to speak to your doctor before you even attempt this.
In many traditions, people are encouraged to take care of their bodies, but there's not a restriction per se. For example, in the tradition I follow, we ask coven members to eat only a light meal before ritual rather than a full one -- but we do not require fasting. We also do not have restrictions on drinking alcohol, as long as it is done only in moderation. None of my coven members smoke, so that's a non-issue. As to sex, as far as I'm concerned, people can have it any time they like, it makes no difference in the context of the rituals of my tradition. Does that mean other traditions have the same rules? Not at all -- each tradition is different.
It's important to note that if you're following a ritual or ceremony that has a specific reason for fasting/abstaining/notdoingwhatever beforehand, it might be wise to follow those guidelines, as long as doing so won't make you ill. For instance, if the tradition believes that fasting brings one closer to the gods, or that abstaining from sexual activity makes the body more pure, then those reasons aren't just arbitrary.
What you might find works for you is a compromise -- the day of the ceremony, take a purifying ritual bath before the ceremony takes place. Meditate a bit, and clear out your mind. Many people find that this helps them, especially if abstaining or fasting isn't part of their normal practice, or wouldn't be healthy for them to do.
