EMI filter for 3v3 over cat5
Generally it's a bad idea to run your regulated voltage through a cable - there's the voltage drop due to the cable. Nevertheless, in certain circumstances you can do this.
At a minimum, I'd suggest a transzorb across the 3V3/0V pair at both ends. As well, a polyfuse at the supply side in series with the 3V3 to limit the short circuit current. Some more bulk capacitance at the load end wouldn't hurt - 47uF or 100uF. Note - the assumption that only fairly small currents are expected - in the order of 100mA.
To get a handle on the expected voltage drop, the nominal resistance of CAT5 is around 12.5 Ohm/100m. At 10m this would be 1.25 Ohm each way (3V3 and 0V wires), so 2.5 Ohms.
Apply Ohm's law: V= IR = 0.1 * 2.5 = 0.25V drop. That's nearly 10%. Depending on your load this could be getting marginal. You could use two or three pairs in parallel to lower this. This should illustrate why sending regulated power over a cable is generally a bad idea.
For example: PoE uses 48V then regulates this at the point of load. Switching regulators are used for power conversion. For your 3.3V at 100mA (my spec) ends up being around 10mA at 48V so the resistive loss is much less: 0.025V drop over 48V is around 0.05%.
A 'simple' solution is to run, say 12V then have a regulator at the load end. Ensure there is a fuse or some other means to limit the current through the wire - failure to do this could create a fire hazard. Then there's the issue of lightning and other transients - tranzorbs are one solution - on both ends of the cable.
An 'off the shelf' solution to your problem would be to use PoE (PoE switches are fairly inexpensive these days or there's PoE injectors) and a PoE 'splitter' or device module which converts PoE back down to a lower voltage. This would work even if you're not using Ethernet - you'd need to choose your pairs carefully though.
I've digressed a bit from your question, but what you ask is a fairly common problem and many learn the hard way that it is not quite as simple as they'd like, thus the suggestion of using PoE.