Use a portable light table.
This is the easiest and the most obvious. Rather than using a highly expensive full-sized light desk, you can use a light table: basically a portable box that you can plug in anywhere. They come in all shapes and sizes, and all price ranges, from low-end hobbyist light tables to high-end professional box. My favorite is the Artograph; I've had mine since art school and it's still plugging on without fail.
Use a photographer's light box.
Light boxes are similar to animators' light tables, but they tend to be flat rather than angled. They also tend to be more expensive, so this may only be a feasible alternative if you already have photography equipment lying around. Your light box (used for viewing photographs and negatives) can serve double duty as an animator's light table, though certain brands can be rather fragile and wouldn't withstand the steady pressure of heavy drawing - especially if you're like me, with a habit of hunching over the light table and resting your arms on it.
Make your own.
With a little plywood, clear or frosted glass or plastic, a handheld florescent light, and a little ingenuity and carpentry, you can build your own light table. It's really just a wooden box with a glass or plastic top and a light inside; you just need to make sure you 1. cut and size the sides so that you can fit the surface plate at a comfortable angle for drawing, 2. either cut a hole in one side to let the light's cord out, or use a battery-operated light. If you're using a battery-operated light, you may want to install hinges on the top surface so you can open it to switch the light on and off. With a corded light, if the switch isn't in easy reach, you can save still save the bulb just by unplugging when you're done. Always remember that hot light bulbs and flammable materials do not mix, and be careful in how you construct your light table.
Improvise.
You'd be surprised at the creative solutions people have found when they don't have access to a light desk or light table. Placing a lamp under a glass coffee table. Drawing on translucent sheets. Even using sunlight in creative ways, when there's no source of readily available (and portable) electricity. All you need is a way to make sure you can see pages of animation layered together, so you can work on keyframes. How you accomplish that depends on the resources you have at hand.
Switch to digital.
A lot of animation software is still cheaper than buying a full-scale light desk, though often far more expensive than simple portable light tables. You can defray software costs by using student versions, or trying the many free animation programs out there. Most 2D animation programs offer an onion-skinning feature that takes the place of a light desk's functionality, allowing you to layer frame visibility and see several in a sequence at once.
These are just a few suggestions for working beyond an animator's standard toolkit. You know what they say: when there's a will, there's a way. If you don't have a light desk, light table, or even the tools to make one, don't let that stop you. Use the resources around you, and find a way to achieve your animation goals.
What are your suggestions for alternatives to using light tables?
