Stones, herbs, numbers, astrological symbols, sigils, talismans, aromas, colors, effigies,... Are just a few of the possible replacements for use of candles. However, if you want to forego using them, you should consider a couple of things. Find ways in your own practice to account for the following and you'll be just fine, candles or no....
-Use of candlelight and flame is a very effective method for helping one achieve the relaxed, altered states of consciousness necessary for most spells or rituals. They also act as a readily available focal point, when time comes for visualization and direction of will. There are several other ways to achieve altered states of consciousness, but the dim, flickering of candle light is an extremely easy and effective way to go about it.
-They also serve as a consumable vessel to pour your will into. Say you were to purchase a candle, and carve your intention into it. As the candle burns and is consumed by the flame, your intent is both literally and metaphysically being transmuted from a physical state, to an energetic state where it can act toward manifesting your goal or desire. In many ways, a well utilized candle can function like putting a spell on auto pilot. The difficulty then, comes only in the initial charging and programming, rather than raising, maintaining, directing and shaping a continuous stream of energies.
-Candles act as a physical embodiment of the spiritual element of fire. Many practitioners find it helpful when casting or performing rituals, to furnish physical embodiments of the elemental energies they're working with. Incense for air, candle for fire, water and salt, etc. Though it's not necessary, it is effective. Especially when first starting out, or when performing an act that falls within that elements' domain. (i.e. having fire physically present for a fire oriented spell, lust, anger, passion, willpower, drive, determination, purification, illumination, etc. The correspondence lists literally never end.)