If you are wishing to research information on the period of history in which Robin Hood may have lived, here are a few notes and links to start on....

WHEN DID ROBIN HOOD EXIST?
The earliest recorded work that mentions Robin Hood actually refers not to Robin at all, but rather to songs written about Robin Hood! "Piers Plowman", a poem by 14th century writer William Langland, is famous among Robin Hood historians for a brief sentence in which a cleric admits that he knows "rymes of Robyn Hood" better than he knows his church prayers:

"If I sholde deye bi this day,' quod he, "me list nought to 1oke.
I kan noght parfitly my Paternoster as the preest it syngeth,
But I kan rymes of Robyn Hood and Randolf Erl of Chestre,
Ac neither of Oure Lord ne of Oure Lady the leeste that evere was maked."

(In today's terms, that would be like a minister saying he has memorized Top Ten songs off the radio, but cannot recite "The Lord's Prayer".)
While this does nothing to pinpoint Robin to any given era, it does prove that stories about Robin Hood existed prior to 1377.
Go here for a complete on-line text copy of "Piers Plowman".

RULERS OF THE TIME PERIOD
Legends and official research differ as to what time period Robin Hood existed in. Traditionally, he has been placed in the era of Richard the Lion Heart who ruled England from 1189 to 1199. Historians who struggle with the possibility of Robin Hood's actual existence prefer to place him during the time of either Edward II or Edward III. Edward II ruled from 1307 to 1327. This Edward was embroiled in several struggles with the Scots, and even had the English people revolt against him. Edward's II's son, Edward III, ruled from 1327-1377 and was considered a popular king. Go here for some historical information on the reigns of English Medieval kings.

FOODS OF THE ERA
While Robin and his men feasted on forbidden venison, the common folks made do with simplier fare. They ate grains, pottages, and "cakes", or rather breads baked on an open hearth, and whatever vegetables or fruits were available depending on the season and the success of the harvest. Sometimes they consumed meat, usually in the form of pork and poultry. Eggs and dairy products were enjoyed mostly in the spring, when such items were more abundant. The wealthy dined on a broader variety of meats and other foods, often seasoned with expensive imported spices, sugar being included as a "spice". As not everyone had an oven, bakers provided the breads and "pasties" so familiar to the modern imagination of what medieval folk dined upon.
For an excellent web site with information, research, and recipes on medieval foods and recipes, go to Master Huen's Booke of Goode Cookery

CLOTHING
Men in tights? Not exactly. While the Victorian and Hollywood image of Robin Hood in his feathered cap and tights makes for a dashing figure, such garments would not exist for several more centuries. Men of the 12th and 13th century wore loose undergarments called braies, with individual leggings called hose pulled up over them. The hose were held in place by "points" attached to the undergarment. This workable arrangement was eventually replaced by about the 15th century by the more convenient of tights and codpiece.
For some authentic reports on medieval legwear, check out these sites:
Chausses And Braies: Garments for the Medieval Leg
Male Clothing and Knightly Armour of the 1250's

ARCHERY
The legend of Robin Hood his skill at archery are unseparatable. The old ballads abound with tales of how easily Robin hit the bullseye, split the wand, or shot through the garland without disturbing a leaf. Robin's famous longbow, manufactured from English yew, did not exist until the 1200's, and for several centuries afterward an English archer with a longbow was a formidable opponent.
Go here for a comprehensive report on the history of the longbow: The Medieval English Longbow