For a vertical mill (You didn't state the type of mill): A decent vise,like a Glacern. No name Chinese ones are not real accurate. Kurt is best,but costly. Don't buy too large a vise for your size mill. It will be heavy,and will cause wear under your table when it slides,and will eat up vertical space on a small mill. A 6" vise with a base under it weighs about 115#,depending upon make. If you aren't able to lift it,get a 4".
A clamping set. I used a Chinese set for years. Their main issue is their threads will pull sideways a little,making it not possible to spin the nuts down freehand. I now have a TECO set. They are much more expensive,but somehow I got a Teco set from Enco on sale for $52.00. Usually they are a few hundred. Much better,properly hardened,the blocks are smoother surfaced,so as to not mar your table. Put paper under Chinese blocks to protect table and add non skid property to them.
A dial test indicator. Chinese ones usually work o.k. if on a budget. I have a Mitutoyo. It is more sensitive than my Last Word indicators.
A set of collets to hold end mills. Chinese ones are not the best,but are o.k. for hobby. I did have ONE that was grossly off center. Most are o.k. for home shop use. If you can afford it,buy a more expensive set.
A set of end mills. Those 20 piece Chinese sets usually work reasonably well. But,I have had them come in nice and sharp,or not quite sharp. It's pot luck. Chinese HSS is harder,and also more brittle than USA end mills. For hobby use,they should be fine,but don't try taking too heavy a cut with them as they can snap off. If you can afford it,an alternative is to buy at least an assortment of HSS Atrax brand end mills from Enco or MSC. Enco always sells cheaper though it is owned by MSC. Atrax is not the best brand,but will be fine for hobby use. They are sharp,and made of decent HSS.
A horizontal/vertical rotary table,with index plates if possible
A decent key type drill chuck,1/2" capacity,with a shank on it that matches your mill
A set of decent drills,fractional 29 pc. set will do. Number drills later on. Buy an American set. Chinese drills often only bother to harden the common fraction sizes.
Some center drills for accurately starting drilled holes.
A 12" steel rule,PEC brand is fine. I like 4R grads(the usual fractions down to 1/64".
A steel square with a 6" beam.Cheap ones are not accurately square. Neither are combination sets. At least buy a name brand. A Mitutoyo would be good. Fowler MIGHT be o.k.. No telling where they were made,though.
A set of parallels.Ground lathe bits look nice,but are not very accurate. a set 1/4" thick is a good general use set. Chinese ones are reasonably accurate for home shop.
Buy or make a fly cutter that uses lathe bits. It will surface large areas better than any end mill can,and doesn't use a lot of power to operate it.