Data below from ebay.com

Need Walkie-Talkies?

Those radios are quite handy. Yard work, clearing snow on driveway, adjusting satellite dish, mowing lawn, so you don't have to scream at your partner on incoming telephone call or to tell favourite TV show is on. Use at shopping mall, on picnic, hiking and slope then you don't get lost... hopefully. On the Cruise ship at open water, your cell phone won't work, walkie talkie will. Just use as a wireless intercom not like an emergency radio to get rescued in remote mountain area.

FRS - Family Radio Service, FRS radios require no licenses. Channels 8 throuh 14,  0.5watts max. power.
GMRS - General Mobile Radio Service require a FCC license in U.S.. FRS/GMRS combo radios sold at store limit radio power to 0.5watts on 8~14ch automatically. Often on 1~7ch shared channels you have to lower radio power manually (on radios more than capable of 0.5watts). 15~22ch are permitted for GMRS only. All FRS/GMRS combo radios require a FCC license in U.S.
Any two or more radios that broadcast on the same frequency (FRS or GMRS) and support the same channels will work together. No need to buy as a pair.

GMRS in Canada?
In Canada, hand-held GMRS radios up to 2 watts have been approved for use since September 2004.
A license is not required in Canada for operation at 2 watts on the GMRS channels.

Which Radio?
Buy durable one, those radios are on action, tossed around. Tap case around before you buy, you could tell thickness of plastic. Motorola and Midland are pretty good in my opinion.

How far?
Don't get fooled by "UP TO xx Miles!!" on the package. Range is all depending on conditions. The number on package is based on The Best Possible Condition.
The Range is always between Shouting and Cellphone.

Typical Range

Rechargeable Battery Pack?
Unless you use radios everyday, those battery pack and drop-in charger aren't needed in my opinion.
Most of radio takes custom pack or standard AAA or AA. Instead of getting radio specific battery pack, consider AA or AAA Ni-MH rechargeable batteries and 1~2Hr quick charger. This way you could get more use of batteries. Take batteries out and charge them on quick charger after use.
Majority of drop-in charger came with radios are not "smart", it will keep charging when even full. Also it may shorten battery life if charged more than 48 hours. If you drain battery pack it takes 8~10hrs to charge on drop-in charger, so keep standard batteries handy. Or just get 2 sets of Ni-MH AA, AAA rechargeables.
Ni-MH Rechargeable Batteries on eBay

Radio Output Power?
Is higher radio power better? Yes and No.
Yes, if you're going to use at wide area, hunting, skiing but 5W radio will not increase the range 10 times more than 0.5W model. Yet 5W radio needs 10+ times power from battery to transmit. This will shorten the operational time on battery. Keep in low power, when it became difficult to reach, switch to high.
No, if you're going to use around house, event in open field or paintball game. You don't have to talk loud when others are closeby.

Channel Scan?
This feature checks all channels (some model has programming capability on channels to be scanned) if in use or not. You may not need this feature if you're using as a pair. Just check the channel before using radios. If someone is using the channel, simply change to other channel.

What is CTCSS?
CTCSS stands for Continuous Tone Coded Squelch System.
Interference-Elimination Codes, sometimes refer to Tone Squelch, TalkGroup or Privacy Code.
It works like Key and Lock on Door. Walkie Talkie transmits sub-audible tone (Key) and opens the door (Lock) on Receiver. For example: Group A on Ch1 no CTCSS, Group B on Ch1 Code1, Group C on Ch1 Code38. Group B won't be bothered by Group A (no Keys) C (wrong Key). Group A can hear all groups because no Lock (incoming door is open).

Keep in mind that this feature doesn't actually protect your privacy. As you see Group A who turned off CTCSS can hear all in the same channel. In addition, anyone who has chosen the same channel and code as you can still transmit to your radio.

What is VOX?
Most of walkie-talkies, you have to press a button (PTT button; Press-To-Talk) in order to talk. Models with a voice-activated (or "VOX") feature begin broadcasting automatically when you speak in to microphone. Some radios require special headset or microphone to use this hands-free function.